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<H1> 7. Other Packages </H1>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC184">7.1 Data Structures</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Various data structures.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC207">7.2 Sorting and Searching</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC225">7.3 Procedures</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Miscellaneous utility procedures.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC235">7.4 Standards Support</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Support for Scheme Standards.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC263">7.5 Session Support</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">REPL and Debugging.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC269">7.6 System Interface</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'system, 'getenv, and other programs.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC276">7.7 Extra-SLIB Packages</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Outside the envelope.</TD></TR>
</TABLE>
<P>
<A NAME="Data Structures"></A>
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<H2> 7.1 Data Structures </H2>
<!--docid::SEC184::-->
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC185">7.1.1 Arrays</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'array</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC186">7.1.2 Subarrays</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'subarray</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC187">7.1.3 Array Mapping</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'array-for-each</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC188">7.1.4 Association Lists</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'alist</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC189">7.1.5 Byte</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'byte</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC190">7.1.6 Byte/Number Conversions</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'byte-number</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC192">7.1.7 MAT-File Format</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'matfile</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC193">7.1.8 Portable Image Files</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'pnm</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC194">7.1.9 Collections</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'collect</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC195">7.1.10 Dynamic Data Type</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'dynamic</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC196">7.1.11 Hash Tables</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'hash-table</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC197">7.1.12 Macroless Object System</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'object</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC204">7.1.16 Priority Queues</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'priority-queue</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC205">7.1.17 Queues</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'queue</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC206">7.1.18 Records</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'record</TD></TR>
</TABLE>
<P>
<A NAME="Arrays"></A>
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</TR></TABLE>
<H3> 7.1.1 Arrays </H3>
<!--docid::SEC185::-->
<P>
<CODE>(require 'array)</CODE>
<A NAME="IDX1094"></A>
</P>
<P>
<A NAME="IDX1095"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array?</B> <I>obj</I>
<DD><P>
Returns <CODE>#t</CODE> if the <VAR>obj</VAR> is an array, and <CODE>#f</CODE> if not.
</P>
</DL>
<EM>Note:</EM> Arrays are not disjoint from other Scheme types. Strings
and vectors also satisfy <CODE>array?</CODE>. A disjoint array predicate can
be written:
<P>
<TABLE><tr><td> </td><td class=example><pre>(define (strict-array? obj)
(and (array? obj) (not (string? obj)) (not (vector? obj))))
</pre></td></tr></table><P>
<A NAME="IDX1096"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array=?</B> <I>array1 array2</I>
<DD><P>
Returns <CODE>#t</CODE> if <VAR>array1</VAR> and <VAR>array2</VAR> have the same rank and shape and the
corresponding elements of <VAR>array1</VAR> and <VAR>array2</VAR> are <CODE>equal?</CODE>.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(array=? (create-array '#(foo) 3 3)
(create-array '#(foo) '(0 2) '(0 2)))
=> #t
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1097"></A>
</P>
<DL>
<DT><U>Function:</U> <B>create-array</B> <I>prototype bound1 bound2 <small>...</small></I>
<DD><P>
Creates and returns an array of type <VAR>prototype</VAR> with dimensions <VAR>bound1</VAR>, <VAR>bound2</VAR>,
<small>...</small> and filled with elements from <VAR>prototype</VAR>. <VAR>prototype</VAR> must be an array,
vector, or string. The implementation-dependent type of the returned
array will be the same as the type of <VAR>prototype</VAR>; except if that would be a
vector or string with non-zero origin, in which case some variety of
array will be returned.
</P>
<P>
If the <VAR>prototype</VAR> has no elements, then the initial contents of the returned
array are unspecified. Otherwise, the returned array will be filled
with the element at the origin of <VAR>prototype</VAR>.
</P>
</DL>
These functions return a prototypical uniform-array enclosing the
optional argument (which must be of the correct type). If the
uniform-array type is supported by the implementation, then it is
returned; defaulting to the next larger precision type; resorting
finally to vector.
<P>
<A NAME="IDX1098"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ac64</B> <I>z</I>
<DD><P>
<A NAME="IDX1099"></A>
<DT><U>Function:</U> <B>ac64</B>
<DD>Returns a high-precision complex uniform-array prototype.
</P>
</DL>
<P>
<A NAME="IDX1100"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ac32</B> <I>z</I>
<DD><P>
<A NAME="IDX1101"></A>
<DT><U>Function:</U> <B>ac32</B>
<DD>Returns a complex uniform-array prototype.
</P>
</DL>
<P>
<A NAME="IDX1102"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ar64</B> <I>x</I>
<DD><P>
<A NAME="IDX1103"></A>
<DT><U>Function:</U> <B>ar64</B>
<DD>Returns a high-precision real uniform-array prototype.
</P>
</DL>
<P>
<A NAME="IDX1104"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ar32</B> <I>x</I>
<DD><P>
<A NAME="IDX1105"></A>
<DT><U>Function:</U> <B>ar32</B>
<DD>Returns a real uniform-array prototype.
</P>
</DL>
<P>
<A NAME="IDX1106"></A>
</P>
<DL>
<DT><U>Function:</U> <B>as64</B> <I>n</I>
<DD><P>
<A NAME="IDX1107"></A>
<DT><U>Function:</U> <B>as64</B>
<DD>Returns an exact signed integer uniform-array prototype with at least
64 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1108"></A>
</P>
<DL>
<DT><U>Function:</U> <B>as32</B> <I>n</I>
<DD><P>
<A NAME="IDX1109"></A>
<DT><U>Function:</U> <B>as32</B>
<DD>Returns an exact signed integer uniform-array prototype with at least
32 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1110"></A>
</P>
<DL>
<DT><U>Function:</U> <B>as16</B> <I>n</I>
<DD><P>
<A NAME="IDX1111"></A>
<DT><U>Function:</U> <B>as16</B>
<DD>Returns an exact signed integer uniform-array prototype with at least
16 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1112"></A>
</P>
<DL>
<DT><U>Function:</U> <B>as8</B> <I>n</I>
<DD><P>
<A NAME="IDX1113"></A>
<DT><U>Function:</U> <B>as8</B>
<DD>Returns an exact signed integer uniform-array prototype with at least
8 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1114"></A>
</P>
<DL>
<DT><U>Function:</U> <B>au64</B> <I>k</I>
<DD><P>
<A NAME="IDX1115"></A>
<DT><U>Function:</U> <B>au64</B>
<DD>Returns an exact non-negative integer uniform-array prototype with at
least 64 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1116"></A>
</P>
<DL>
<DT><U>Function:</U> <B>au32</B> <I>k</I>
<DD><P>
<A NAME="IDX1117"></A>
<DT><U>Function:</U> <B>au32</B>
<DD>Returns an exact non-negative integer uniform-array prototype with at
least 32 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1118"></A>
</P>
<DL>
<DT><U>Function:</U> <B>au16</B> <I>k</I>
<DD><P>
<A NAME="IDX1119"></A>
<DT><U>Function:</U> <B>au16</B>
<DD>Returns an exact non-negative integer uniform-array prototype with at
least 16 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1120"></A>
</P>
<DL>
<DT><U>Function:</U> <B>au8</B> <I>k</I>
<DD><P>
<A NAME="IDX1121"></A>
<DT><U>Function:</U> <B>au8</B>
<DD>Returns an exact non-negative integer uniform-array prototype with at
least 8 bits of precision.
</P>
</DL>
<P>
<A NAME="IDX1122"></A>
</P>
<DL>
<DT><U>Function:</U> <B>at1</B> <I>bool</I>
<DD><P>
<A NAME="IDX1123"></A>
<DT><U>Function:</U> <B>at1</B>
<DD>Returns a boolean uniform-array prototype.
</P>
</DL>
When constructing an array, <VAR>bound</VAR> is either an inclusive range of
indices expressed as a two element list, or an upper bound expressed as
a single integer. So
<P>
<TABLE><tr><td> </td><td class=example><pre>(create-array '#(foo) 3 3) == (create-array '#(foo) '(0 2) '(0 2))
</pre></td></tr></table><P>
<A NAME="IDX1124"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-shared-array</B> <I>array mapper bound1 bound2 <small>...</small></I>
<DD><P>
<CODE>make-shared-array</CODE> can be used to create shared subarrays of other
arrays. The <VAR>mapper</VAR> is a function that translates coordinates in
the new array into coordinates in the old array. A <VAR>mapper</VAR> must be
linear, and its range must stay within the bounds of the old array, but
it can be otherwise arbitrary. A simple example:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(define fred (create-array '#(#f) 8 8))
(define freds-diagonal
(make-shared-array fred (lambda (i) (list i i)) 8))
(array-set! freds-diagonal 'foo 3)
(array-ref fred 3 3)
=> FOO
(define freds-center
(make-shared-array fred (lambda (i j) (list (+ 3 i) (+ 3 j)))
2 2))
(array-ref freds-center 0 0)
=> FOO
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1125"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-rank</B> <I>obj</I>
<DD><P>
Returns the number of dimensions of <VAR>obj</VAR>. If <VAR>obj</VAR> is not an array, 0 is
returned.
</P>
</DL>
<P>
<A NAME="IDX1126"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-shape</B> <I>array</I>
<DD><P>
Returns a list of inclusive bounds.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(array-shape (create-array '#() 3 5))
=> ((0 2) (0 4))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1127"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-dimensions</B> <I>array</I>
<DD><P>
<CODE>array-dimensions</CODE> is similar to <CODE>array-shape</CODE> but replaces
elements with a 0 minimum with one greater than the maximum.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(array-dimensions (create-array '#() 3 5))
=> (3 5)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1128"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-in-bounds?</B> <I>array index1 index2 <small>...</small></I>
<DD><P>
Returns <CODE>#t</CODE> if its arguments would be acceptable to
<CODE>array-ref</CODE>.
</P>
</DL>
<P>
<A NAME="IDX1129"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-ref</B> <I>array index1 index2 <small>...</small></I>
<DD><P>
Returns the (<VAR>index1</VAR>, <VAR>index2</VAR>, <small>...</small>) element of <VAR>array</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1130"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>array-set!</B> <I>array obj index1 index2 <small>...</small></I>
<DD><P>
Stores <VAR>obj</VAR> in the (<VAR>index1</VAR>, <VAR>index2</VAR>, <small>...</small>) element of <VAR>array</VAR>. The value returned
by <CODE>array-set!</CODE> is unspecified.
</P>
</DL>
<P>
<A NAME="Subarrays"></A>
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</TR></TABLE>
<H3> 7.1.2 Subarrays </H3>
<!--docid::SEC186::-->
<P>
<CODE>(require 'subarray)</CODE>
<A NAME="IDX1131"></A>
</P>
<P>
<A NAME="IDX1132"></A>
</P>
<DL>
<DT><U>Function:</U> <B>subarray</B> <I>array select <small>...</small></I>
<DD><P>
selects a subset of an array. For <VAR>array</VAR> of rank n, there must be at least
n <VAR>selects</VAR> arguments. For 0 <= <I>j</I> < n, <VAR>selects</VAR><I>j</I> is either an integer, a
list of two integers within the range for the <I>j</I>th index, or #f.
</P>
<P>
When <VAR>selects</VAR><I>j</I> is a list of two integers, then the <I>j</I>th index is
restricted to that subrange in the returned array.
</P>
<P>
When <VAR>selects</VAR><I>j</I> is #f, then the full range of the <I>j</I>th index is
accessible in the returned array. An elided argument is equivalent to #f.
</P>
<P>
When <VAR>selects</VAR><I>j</I> is an integer, then the rank of the returned array is
less than <VAR>array</VAR>, and only elements whose <I>j</I>th index equals <VAR>selects</VAR><I>j</I> are
shared.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>> (define ra '#2A((a b c) (d e f)))
#<unspecified>
> (subarray ra 0 #f)
#1A(a b c)
> (subarray ra 1 #f)
#1A(d e f)
> (subarray ra #f 1)
#1A(b e)
> (subarray ra '(0 1) #f)
#2A((a b c) (d e f))
> (subarray ra #f '(0 1))
#2A((a b) (d e))
> (subarray ra #f '(1 2))
#2A((b c) (e f))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1133"></A>
</P>
<DL>
<DT><U>Function:</U> <B>subarray0</B> <I>array select <small>...</small></I>
<DD><P>
Behaves like subarray, but aligns the returned array origin to
0 <small>...</small>.
</P>
</DL>
<P>
<A NAME="IDX1134"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-align</B> <I>array coord <small>...</small></I>
<DD><P>
Returns an array shared with <VAR>array</VAR> but with a different origin. The <VAR>coords</VAR>
are the exact integer coordinates of the new origin. Indexes
corresponding to missing or #f coordinates are not realigned.
</P>
<P>
For example:
<TABLE><tr><td> </td><td class=example><pre>(define ra2 (create-array '#(5) '(5 9) '(-4 0)))
(array-shape ra2) => ((5 9) (-4 0))
(array-shape (array-align ra2 0 0)) => ((0 4) (0 4))
(array-shape (array-align ra2 0)) => ((0 4) (-4 0))
(array-shape (array-align ra2)) => ((5 9) (-4 0))
(array-shape (array-align ra2 0 #f)) => ((0 4) (-4 0))
(array-shape (array-align ra2 #f 0)) => ((5 9) (0 4))
</pre></td></tr></table></DL>
<A NAME="IDX1135"></A>
<DL>
<DT><U>Function:</U> <B>array-trim</B> <I>array trim <small>...</small></I>
<DD><P>
Returns a subarray sharing contents with <VAR>array</VAR> except for slices removed
from either side of each dimension. Each of the <VAR>trims</VAR> is an exact
integer indicating how much to trim. A positive <VAR>s</VAR> trims the
data from the lower end and reduces the upper bound of the result; a
negative <VAR>s</VAR> trims from the upper end and increases the lower
bound.
</P>
<P>
For example:
<TABLE><tr><td> </td><td class=example><pre>(array-trim '#(0 1 2 3 4) 1) => #1A(1 2 3 4) ;; shape is ((0 3))
(array-trim '#(0 1 2 3 4) -1) => #1A(0 1 2 3) ;; shape is ((1 4))
(require 'array-for-each)
(define (centered-difference ra)
(array-map - (array-trim ra 1) (array-trim ra -1)))
(define (forward-difference ra)
(array-map - (array-trim ra 1) ra))
(define (backward-difference ra)
(array-map - ra (array-trim ra -1)))
(centered-difference '#(0 1 3 5 9 22))
=> #1A(3 4 6 17) ;;shape is ((1 4))
(backward-difference '#(0 1 3 5 9 22))
=> #1A(1 2 2 4 13) ;; shape is ((1 5))
(forward-difference '#(0 1 3 5 9 22))
=> #(1 2 2 4 13) ;; shape is ((0 4))
</pre></td></tr></table></DL>
<P>
<A NAME="Array Mapping"></A>
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<H3> 7.1.3 Array Mapping </H3>
<!--docid::SEC187::-->
<P>
<CODE>(require 'array-for-each)</CODE>
<A NAME="IDX1136"></A>
</P>
<P>
<A NAME="IDX1137"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>array-map!</B> <I>array0 proc array1 <small>...</small></I>
<DD><P>
<VAR>array1</VAR>, <small>...</small> must have the same number of dimensions as
<VAR>array0</VAR> and have a range for each index which includes the range
for the corresponding index in <VAR>array0</VAR>. <VAR>proc</VAR> is applied to
each tuple of elements of <VAR>array1</VAR> <small>...</small> and the result is stored
as the corresponding element in <VAR>array0</VAR>. The value returned is
unspecified. The order of application is unspecified.
</P>
</DL>
<P>
<A NAME="IDX1138"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-map</B> <I>prototype proc array1 array2 <small>...</small></I>
<DD><P>
<VAR>array2</VAR>, <small>...</small> must have the same number of dimensions as
<VAR>array1</VAR> and have a range for each index which includes the
range for the corresponding index in <VAR>array1</VAR>. <VAR>proc</VAR> is
applied to each tuple of elements of <VAR>array1</VAR>, <VAR>array2</VAR>,
<small>...</small> and the result is stored as the corresponding element in a
new array of type <VAR>prototype</VAR>. The new array is returned. The
order of application is unspecified.
</P>
</DL>
<P>
<A NAME="IDX1139"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-for-each</B> <I>proc array0 <small>...</small></I>
<DD><P>
<VAR>proc</VAR> is applied to each tuple of elements of <VAR>array0</VAR> <small>...</small>
in row-major order. The value returned is unspecified.
</P>
</DL>
<P>
<A NAME="IDX1140"></A>
</P>
<DL>
<DT><U>Function:</U> <B>array-indexes</B> <I>array</I>
<DD><P>
Returns an array of lists of indexes for <VAR>array</VAR> such that, if
<VAR>li</VAR> is a list of indexes for which <VAR>array</VAR> is defined,
(equal? <VAR>li</VAR> (apply array-ref (array-indexes <VAR>array</VAR>)
<VAR>li</VAR>)).
</P>
</DL>
<P>
<A NAME="IDX1141"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>array-index-map!</B> <I>array proc</I>
<DD><P>
applies <VAR>proc</VAR> to the indices of each element of <VAR>array</VAR> in
turn, storing the result in the corresponding element. The value
returned and the order of application are unspecified.
</P>
<P>
One can implement <VAR>array-indexes</VAR> as
<TABLE><tr><td> </td><td class=example><pre>(define (array-indexes array)
(let ((ra (apply create-array '#() (array-shape array))))
(array-index-map! ra (lambda x x))
ra))
</pre></td></tr></table>Another example:
<TABLE><tr><td> </td><td class=example><pre>(define (apl:index-generator n)
(let ((v (make-vector n 1)))
(array-index-map! v (lambda (i) i))
v))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1142"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>array-copy!</B> <I>source destination</I>
<DD><P>
Copies every element from vector or array <VAR>source</VAR> to the
corresponding element of <VAR>destination</VAR>. <VAR>destination</VAR> must
have the same rank as <VAR>source</VAR>, and be at least as large in each
dimension. The order of copying is unspecified.
</P>
</DL>
<P>
<A NAME="Association Lists"></A>
<HR SIZE="6">
<A NAME="SEC188"></A>
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</TR></TABLE>
<H3> 7.1.4 Association Lists </H3>
<!--docid::SEC188::-->
<P>
<CODE>(require 'alist)</CODE>
<A NAME="IDX1143"></A>
</P>
<P>
Alist functions provide utilities for treating a list of key-value pairs
as an associative database. These functions take an equality predicate,
<VAR>pred</VAR>, as an argument. This predicate should be repeatable,
symmetric, and transitive.
</P>
<P>
Alist functions can be used with a secondary index method such as hash
tables for improved performance.
</P>
<P>
<A NAME="IDX1144"></A>
</P>
<DL>
<DT><U>Function:</U> <B>predicate->asso</B> <I>pred</I>
<DD><P>
Returns an <EM>association function</EM> (like <CODE>assq</CODE>, <CODE>assv</CODE>, or
<A NAME="IDX1145"></A>
<CODE>assoc</CODE>) corresponding to <VAR>pred</VAR>. The returned function
returns a key-value pair whose key is <CODE>pred</CODE>-equal to its first
argument or <CODE>#f</CODE> if no key in the alist is <VAR>pred</VAR>-equal to the
first argument.
</P>
</DL>
<P>
<A NAME="IDX1146"></A>
</P>
<DL>
<DT><U>Function:</U> <B>alist-inquirer</B> <I>pred</I>
<DD><P>
Returns a procedure of 2 arguments, <VAR>alist</VAR> and <VAR>key</VAR>, which
returns the value associated with <VAR>key</VAR> in <VAR>alist</VAR> or <CODE>#f</CODE> if
<VAR>key</VAR> does not appear in <VAR>alist</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1147"></A>
</P>
<DL>
<DT><U>Function:</U> <B>alist-associator</B> <I>pred</I>
<DD><P>
Returns a procedure of 3 arguments, <VAR>alist</VAR>, <VAR>key</VAR>, and
<VAR>value</VAR>, which returns an alist with <VAR>key</VAR> and <VAR>value</VAR>
associated. Any previous value associated with <VAR>key</VAR> will be
lost. This returned procedure may or may not have side effects on its
<VAR>alist</VAR> argument. An example of correct usage is:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(define put (alist-associator string-ci=?))
(define alist '())
(set! alist (put alist "Foo" 9))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1148"></A>
</P>
<DL>
<DT><U>Function:</U> <B>alist-remover</B> <I>pred</I>
<DD><P>
Returns a procedure of 2 arguments, <VAR>alist</VAR> and <VAR>key</VAR>, which
returns an alist with an association whose <VAR>key</VAR> is key removed.
This returned procedure may or may not have side effects on its
<VAR>alist</VAR> argument. An example of correct usage is:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(define rem (alist-remover string-ci=?))
(set! alist (rem alist "foo"))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1149"></A>
</P>
<DL>
<DT><U>Function:</U> <B>alist-map</B> <I>proc alist</I>
<DD><P>
Returns a new association list formed by mapping <VAR>proc</VAR> over the
keys and values of <VAR>alist</VAR>. <VAR>proc</VAR> must be a function of 2
arguments which returns the new value part.
</P>
</DL>
<P>
<A NAME="IDX1150"></A>
</P>
<DL>
<DT><U>Function:</U> <B>alist-for-each</B> <I>proc alist</I>
<DD><P>
Applies <VAR>proc</VAR> to each pair of keys and values of <VAR>alist</VAR>.
<VAR>proc</VAR> must be a function of 2 arguments. The returned value is
unspecified.
</P>
</DL>
<P>
<A NAME="Byte"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.1.5 Byte </H3>
<!--docid::SEC189::-->
<P>
<CODE>(require 'byte)</CODE>
<A NAME="IDX1151"></A>
</P>
<P>
Some algorithms are expressed in terms of arrays of small integers.
Using Scheme strings to implement these arrays is not portable vis-a-vis
the correspondence between integers and characters and non-ascii
character sets. These functions abstract the notion of a <EM>byte</EM>.
<A NAME="IDX1152"></A>
<A NAME="IDX1153"></A>
</P>
<P>
<A NAME="IDX1154"></A>
</P>
<DL>
<DT><U>Function:</U> <B>byte-ref</B> <I>bytes k</I>
<DD><P>
<VAR>k</VAR> must be a valid index of <VAR>bytes</VAR>. <CODE>byte-ref</CODE> returns byte <VAR>k</VAR> of <VAR>bytes</VAR> using
zero-origin indexing.
</P>
</DL>
<P>
<A NAME="IDX1155"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>byte-set!</B> <I>bytes k byte</I>
<DD><P>
<VAR>k</VAR> must be a valid index of <VAR>bytes</VAR>, and <VAR>byte</VAR> must be a small
nonnegative integer. <CODE>byte-set!</CODE> stores <VAR>byte</VAR> in element <VAR>k</VAR> of <VAR>bytes</VAR> and
returns an unspecified value.
</P>
</DL>
<P>
<A NAME="IDX1156"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-bytes</B> <I>k byte</I>
<DD><P>
<A NAME="IDX1157"></A>
<DT><U>Function:</U> <B>make-bytes</B> <I>k</I>
<DD><CODE>make-bytes</CODE> returns a newly allocated byte-array of length <VAR>k</VAR>. If <VAR>byte</VAR> is
given, then all elements of the byte-array are initialized to <VAR>byte</VAR>,
otherwise the contents of the byte-array are unspecified.
</P>
</DL>
<P>
<A NAME="IDX1158"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes-length</B> <I>bytes</I>
<DD><P>
<CODE>bytes-length</CODE> returns length of byte-array <VAR>bytes</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1159"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes</B> <I>byte <small>...</small></I>
<DD><P>
Returns a newly allocated byte-array composed of the small
nonnegative arguments.
</P>
</DL>
<P>
<A NAME="IDX1160"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes->list</B> <I>bytes</I>
<DD><P>
<CODE>bytes->list</CODE> returns a newly allocated list of the bytes that make up the
given byte-array.
</P>
</DL>
<P>
<A NAME="IDX1161"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list->bytes</B> <I>bytes</I>
<DD><P>
<CODE>list->bytes</CODE> returns a newly allocated byte-array formed from the small
nonnegative integers in the list <VAR>bytes</VAR>.
</P>
</DL>
<CODE>Bytes->list</CODE> and <CODE>list->bytes</CODE> are inverses so far as
<CODE>equal?</CODE> is concerned.
<A NAME="IDX1162"></A>
<P>
<A NAME="IDX1163"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes-copy</B> <I>bytes</I>
<DD><P>
Returns a newly allocated copy of the given <VAR>bytes</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1164"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>bytes-reverse!</B> <I>bytes</I>
<DD><P>
Reverses the order of byte-array <VAR>bytes</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1165"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes-reverse</B> <I>bytes</I>
<DD><P>
Returns a newly allocated bytes-array consisting of the elements of
<VAR>bytes</VAR> in reverse order.
</P>
</DL>
<A NAME="IDX1166"></A>
Input and output of bytes should be with ports opened in <EM>binary</EM>
<A NAME="IDX1167"></A>
mode (see section <A HREF="slib_2.html#SEC16">2.3 Input/Output</A>). Calling <CODE>open-file</CODE> with 'rb or
<A NAME="IDX1168"></A>
'wb modes argument will return a binary port if the Scheme
implementation supports it.
<P>
<A NAME="IDX1169"></A>
</P>
<DL>
<DT><U>Function:</U> <B>write-byte</B> <I>byte port</I>
<DD><P>
<A NAME="IDX1170"></A>
<DT><U>Function:</U> <B>write-byte</B> <I>byte</I>
<DD>Writes the byte <VAR>byte</VAR> (not an external representation of the byte) to
the given <VAR>port</VAR> and returns an unspecified value. The <VAR>port</VAR> argument may
be omitted, in which case it defaults to the value returned by
<CODE>current-output-port</CODE>.
<A NAME="IDX1171"></A>
</P>
</DL>
<P>
<A NAME="IDX1172"></A>
</P>
<DL>
<DT><U>Function:</U> <B>read-byte</B> <I>port</I>
<DD><P>
<A NAME="IDX1173"></A>
<DT><U>Function:</U> <B>read-byte</B>
<DD>Returns the next byte available from the input <VAR>port</VAR>, updating the <VAR>port</VAR>
to point to the following byte. If no more bytes are available, an
end-of-file object is returned. <VAR>port</VAR> may be omitted, in which case it
defaults to the value returned by <CODE>current-input-port</CODE>.
<A NAME="IDX1174"></A>
</P>
</DL>
When reading and writing binary numbers with <CODE>read-bytes</CODE> and
<CODE>write-bytes</CODE>, the sign of the length argument determines the
endianness (order) of bytes. Positive treats them as big-endian,
the first byte input or output is highest order. Negative treats
them as little-endian, the first byte input or output is the lowest
order.
<P>
Once read in, SLIB treats byte sequences as big-endian. The
multi-byte sequences produced and used by number conversion routines
see section <A HREF="slib_7.html#SEC190">7.1.6 Byte/Number Conversions</A> are always big-endian.
</P>
<P>
<A NAME="IDX1175"></A>
</P>
<DL>
<DT><U>Function:</U> <B>read-bytes</B> <I>n port</I>
<DD><P>
<A NAME="IDX1176"></A>
<DT><U>Function:</U> <B>read-bytes</B> <I>n</I>
<DD><CODE>read-bytes</CODE> returns a newly allocated bytes-array filled with
<CODE>(abs <VAR>n</VAR>)</CODE> bytes read from <VAR>port</VAR>. If <VAR>n</VAR> is positive, then
the first byte read is stored at index 0; otherwise the last byte
read is stored at index 0. Note that the length of the returned
string will be less than <CODE>(abs <VAR>n</VAR>)</CODE> if <VAR>port</VAR> reaches
end-of-file.
</P>
<P>
<VAR>port</VAR> may be omitted, in which case it defaults to the value returned
by <CODE>current-input-port</CODE>.
</P>
</DL>
<P>
<A NAME="IDX1177"></A>
</P>
<DL>
<DT><U>Function:</U> <B>write-bytes</B> <I>bytes n port</I>
<DD><P>
<A NAME="IDX1178"></A>
<DT><U>Function:</U> <B>write-bytes</B> <I>bytes n</I>
<DD><CODE>write-bytes</CODE> writes <CODE>(abs <VAR>n</VAR>)</CODE> bytes to output-port <VAR>port</VAR>. If <VAR>n</VAR> is
positive, then the first byte written is index 0 of <VAR>bytes</VAR>; otherwise
the last byte written is index 0 of <VAR>bytes</VAR>. <CODE>write-bytes</CODE> returns an unspecified
value.
</P>
<P>
<VAR>port</VAR> may be omitted, in which case it defaults to the value returned
by <CODE>current-output-port</CODE>.
</P>
</DL>
<CODE>substring-read!</CODE> and <CODE>substring-write</CODE> provide
lower-level procedures for reading and writing blocks of bytes. The
relative size of <VAR>start</VAR> and <VAR>end</VAR> determines the order of
writing.
<P>
<A NAME="IDX1179"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>substring-read!</B> <I>string start end port</I>
<DD><P>
<A NAME="IDX1180"></A>
<DT><U>Procedure:</U> <B>substring-read!</B> <I>string start end</I>
<DD>Fills <VAR>string</VAR> with up to <CODE>(abs (- <VAR>start</VAR> <VAR>end</VAR>))</CODE> bytes
read from <VAR>port</VAR>. The first byte read is stored at index <VAR>string</VAR>.
<CODE>substring-read!</CODE> returns the number of bytes read.
</P>
<P>
<VAR>port</VAR> may be omitted, in which case it defaults to the value returned
by <CODE>current-input-port</CODE>.
</P>
</DL>
<P>
<A NAME="IDX1181"></A>
</P>
<DL>
<DT><U>Function:</U> <B>substring-write</B> <I>string start end port</I>
<DD><P>
<A NAME="IDX1182"></A>
<DT><U>Function:</U> <B>substring-write</B> <I>string start end</I>
<DD><CODE>substring-write</CODE> writes <CODE>(abs (- <VAR>start</VAR> <VAR>end</VAR>))</CODE> bytes to
output-port <VAR>port</VAR>. The first byte written is index <VAR>start</VAR> of <VAR>string</VAR>. <CODE>substring-write</CODE>
returns the number of bytes written.
</P>
<P>
<VAR>port</VAR> may be omitted, in which case it defaults to the value returned
by <CODE>current-output-port</CODE>.
</P>
</DL>
<P>
<A NAME="Byte/Number Conversions"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.1.6 Byte/Number Conversions </H3>
<!--docid::SEC190::-->
<P>
<CODE>(require 'byte-number)</CODE>
<A NAME="IDX1183"></A>
</P>
<P>
The multi-byte sequences produced and used by numeric conversion
routines are always big-endian. Endianness can be changed during
reading and writing bytes using <CODE>read-bytes</CODE> and
<CODE>write-bytes</CODE> See section <A HREF="slib_7.html#SEC189">read-bytes</A>.
</P>
<P>
The sign of the length argument to bytes/integer conversion
procedures determines the signedness of the number.
</P>
<P>
<A NAME="IDX1184"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes->integer</B> <I>bytes n</I>
<DD><P>
Converts the first <CODE>(abs <VAR>n</VAR>)</CODE> bytes of big-endian <VAR>bytes</VAR> array
to an integer. If <VAR>n</VAR> is negative then the integer coded by the
bytes are treated as two's-complement (can be negative).
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(bytes->integer (bytes 0 0 0 15) -4) => 15
(bytes->integer (bytes 0 0 0 15) 4) => 15
(bytes->integer (bytes 255 255 255 255) -4) => -1
(bytes->integer (bytes 255 255 255 255) 4) => 4294967295
(bytes->integer (bytes 128 0 0 0) -4) => -2147483648
(bytes->integer (bytes 128 0 0 0) 4) => 2147483648
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1185"></A>
</P>
<DL>
<DT><U>Function:</U> <B>integer->bytes</B> <I>n len</I>
<DD><P>
Converts the integer <VAR>n</VAR> to a byte-array of <CODE>(abs <VAR>n</VAR>)</CODE>
bytes. If <VAR>n</VAR> and <VAR>len</VAR> are both negative, then the bytes in the
returned array are coded two's-complement.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(bytes->list (integer->bytes 15 -4)) => (0 0 0 15)
(bytes->list (integer->bytes 15 4)) => (0 0 0 15)
(bytes->list (integer->bytes -1 -4)) => (255 255 255 255)
(bytes->list (integer->bytes 4294967295 4)) => (255 255 255 255)
(bytes->list (integer->bytes -2147483648 -4)) => (128 0 0 0)
(bytes->list (integer->bytes 2147483648 4)) => (128 0 0 0)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1186"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes->ieee-float</B> <I>bytes</I>
<DD><P>
<VAR>bytes</VAR> must be a 4-element byte-array. <CODE>bytes->ieee-float</CODE> calculates and returns the
value of <VAR>bytes</VAR> interpreted as a big-endian IEEE 4-byte (32-bit) number.
</P>
</DL>
<TABLE><tr><td> </td><td class=example><pre>(bytes->ieee-float (bytes #x40 0 0 0)) => 2.0
(bytes->ieee-float (bytes #x40 #xd0 0 0)) => 6.5
(bytes->ieee-float (bytes #xc0 #xd0 0 0)) => -6.5
(bytes->ieee-float (bytes 0 #x80 0 0)) => 11.754943508222875e-39
(bytes->ieee-float (bytes 0 #x40 0 0)) => 5.877471754111437e-39
(bytes->ieee-float (bytes 0 0 0 1)) => 1.401298464324817e-45
(bytes->ieee-float (bytes #xff #x80 0 0)) => -1/0
(bytes->ieee-float (bytes #x7f #x80 0 0)) => 1/0
(bytes->ieee-float (bytes #x7f #x80 0 1)) => 0/0
</pre></td></tr></table><P>
<A NAME="IDX1187"></A>
</P>
<DL>
<DT><U>Function:</U> <B>bytes->ieee-double</B> <I>bytes</I>
<DD><P>
<VAR>bytes</VAR> must be a 8-element byte-array. <CODE>bytes->ieee-double</CODE> calculates and returns the
value of <VAR>bytes</VAR> interpreted as a big-endian IEEE 8-byte (64-bit) number.
</P>
</DL>
<TABLE><tr><td> </td><td class=example><pre>(bytes->ieee-double (bytes 0 0 0 0 0 0 0 0)) => 0.0
(bytes->ieee-double (bytes #x40 0 0 0 0 0 0 0)) => 2
(bytes->ieee-double (bytes #x40 #x1A 0 0 0 0 0 0)) => 6.5
(bytes->ieee-double (bytes #xC0 #x1A 0 0 0 0 0 0)) => -6.5
(bytes->ieee-double (bytes 0 8 0 0 0 0 0 0)) => 11.125369292536006e-309
(bytes->ieee-double (bytes 0 4 0 0 0 0 0 0)) => 5.562684646268003e-309
(bytes->ieee-double (bytes 0 0 0 0 0 0 0 1)) => 4.0e-324
(bytes->ieee-double (bytes #xFF #xF0 0 0 0 0 0 0)) => -1/0
(bytes->ieee-double (bytes #x7F #xF0 0 0 0 0 0 0)) => 1/0
(bytes->ieee-double (bytes #x7F #xF8 0 0 0 0 0 0)) => 0/0
</pre></td></tr></table><P>
<A NAME="IDX1188"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ieee-float->bytes</B> <I>x</I>
<DD><P>
Returns a 4-element byte-array encoding the IEEE single-precision
floating-point of <VAR>x</VAR>.
</P>
</DL>
<TABLE><tr><td> </td><td class=example><pre>(bytes->list (ieee-float->bytes 2.0)) => (64 0 0 0)
(bytes->list (ieee-float->bytes 6.5)) => (64 208 0 0)
(bytes->list (ieee-float->bytes -6.5)) => (192 208 0 0)
(bytes->list (ieee-float->bytes 11.754943508222875e-39)) => ( 0 128 0 0)
(bytes->list (ieee-float->bytes 5.877471754111438e-39)) => ( 0 64 0 0)
(bytes->list (ieee-float->bytes 1.401298464324817e-45)) => ( 0 0 0 1)
(bytes->list (ieee-float->bytes -1/0)) => (255 128 0 0)
(bytes->list (ieee-float->bytes 1/0)) => (127 128 0 0)
(bytes->list (ieee-float->bytes 0/0)) => (127 128 0 1)
</pre></td></tr></table><P>
<A NAME="IDX1189"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ieee-double->bytes</B> <I>x</I>
<DD><P>
Returns a 8-element byte-array encoding the IEEE double-precision
floating-point of <VAR>x</VAR>.
</P>
</DL>
<TABLE><tr><td> </td><td class=example><pre>(bytes->list (ieee-double->bytes 2.0)) => (64 0 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes 6.5)) => (64 26 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes -6.5)) => (192 26 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes 11.125369292536006e-309))
=> ( 0 8 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes 5.562684646268003e-309))
=> ( 0 4 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes 4.0e-324))
=> ( 0 0 0 0 0 0 0 1)
(bytes->list (ieee-double->bytes -1/0)) => (255 240 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes 1/0)) => (127 240 0 0 0 0 0 0)
(bytes->list (ieee-double->bytes 0/0)) => (127 248 0 0 0 0 0 0)
</pre></td></tr></table><P>
<A NAME="SEC191"></A>
<H4> Byte Collation Order </H4>
<!--docid::SEC191::-->
<P>
The <CODE>string<?</CODE> ordering of big-endian byte-array
representations of fixed and IEEE floating-point numbers agrees with
the numerical ordering only when those numbers are non-negative.
</P>
<P>
Straighforward modification of these formats can extend the
byte-collating order to work for their entire ranges. This
agreement enables the full range of numbers as keys in
<EM>indexed-sequential-access-method</EM> databases.
<A NAME="IDX1190"></A>
</P>
<P>
<A NAME="IDX1191"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>integer-byte-collate!</B> <I>byte-vector</I>
<DD><P>
Modifies sign bit of <VAR>byte-vector</VAR> so that <CODE>string<?</CODE> ordering of
two's-complement byte-vectors matches numerical order. <CODE>integer-byte-collate!</CODE> returns
<VAR>byte-vector</VAR> and is its own functional inverse.
</P>
</DL>
<P>
<A NAME="IDX1192"></A>
</P>
<DL>
<DT><U>Function:</U> <B>integer-byte-collate</B> <I>byte-vector</I>
<DD><P>
Returns copy of <VAR>byte-vector</VAR> with sign bit modified so that <CODE>string<?</CODE>
ordering of two's-complement byte-vectors matches numerical order.
<CODE>integer-byte-collate</CODE> is its own functional inverse.
</P>
</DL>
<P>
<A NAME="IDX1193"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>ieee-byte-collate!</B> <I>byte-vector</I>
<DD><P>
Modifies <VAR>byte-vector</VAR> so that <CODE>string<?</CODE> ordering of IEEE floating-point
byte-vectors matches numerical order. <CODE>ieee-byte-collate!</CODE> returns <VAR>byte-vector</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1194"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>ieee-byte-decollate!</B> <I>byte-vector</I>
<DD><P>
Given <VAR>byte-vector</VAR> modified by <CODE>IEEE-byte-collate!</CODE>, reverses the <VAR>byte-vector</VAR>
modifications.
</P>
</DL>
<P>
<A NAME="IDX1195"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ieee-byte-collate</B> <I>byte-vector</I>
<DD><P>
Returns copy of <VAR>byte-vector</VAR> encoded so that <CODE>string<?</CODE> ordering of IEEE
floating-point byte-vectors matches numerical order.
</P>
</DL>
<P>
<A NAME="IDX1196"></A>
</P>
<DL>
<DT><U>Function:</U> <B>ieee-byte-decollate</B> <I>byte-vector</I>
<DD><P>
Given <VAR>byte-vector</VAR> returned by <CODE>IEEE-byte-collate</CODE>, reverses the <VAR>byte-vector</VAR>
modifications.
</P>
</DL>
<P>
<A NAME="MAT-File Format"></A>
<HR SIZE="6">
<A NAME="SEC192"></A>
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</TR></TABLE>
<H3> 7.1.7 MAT-File Format </H3>
<!--docid::SEC192::-->
<P>
<CODE>(require 'matfile)</CODE>
<A NAME="IDX1197"></A>
<A NAME="IDX1198"></A>
</P>
<P>
<A HREF="http://www.mathworks.com/access/helpdesk/help/pdf_doc/matlab/matfile_format.pdf">http://www.mathworks.com/access/helpdesk/help/pdf_doc/matlab/matfile_format.pdf</A>
</P>
<P>
This package reads MAT-File Format version 4 (MATLAB) binary data
files. MAT-files written from big-endian or little-endian computers
having IEEE format numbers are currently supported. Support for files
written from VAX or Cray machines could also be added.
</P>
<P>
The numeric and text matrix types handled; support for <EM>sparse</EM>
<A NAME="IDX1199"></A>
matrices awaits a sample file.
</P>
<P>
<A NAME="IDX1200"></A>
</P>
<DL>
<DT><U>Function:</U> <B>matfile:read</B> <I>filename</I>
<DD><VAR>filename</VAR> should be a string naming an existing file containing a
MATLAB Version 4 MAT-File. The <CODE>matfile:read</CODE> procedure reads matrices from the
file and returns a list of the results; a list of the name string and
array for each matrix.
</DL>
<P>
<A NAME="IDX1201"></A>
</P>
<DL>
<DT><U>Function:</U> <B>matfile:load</B> <I>filename</I>
<DD><VAR>filename</VAR> should be a string naming an existing file containing a
MATLAB Version 4 MAT-File. The <CODE>matfile:load</CODE> procedure reads matrices from the
file and defines the <CODE>string-ci->symbol</CODE> for each matrix to its
corresponding array. <CODE>matfile:load</CODE> returns a list of the symbols defined.
</DL>
<P>
<A NAME="Portable Image Files"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.1.8 Portable Image Files </H3>
<!--docid::SEC193::-->
<P>
<CODE>(require 'pnm)</CODE>
<A NAME="IDX1202"></A>
</P>
<P>
<A NAME="IDX1203"></A>
</P>
<DL>
<DT><U>Function:</U> <B>pnm:type-dimensions</B> <I>path</I>
<DD><P>
The string <VAR>path</VAR> must name a <EM>portable bitmap graphics</EM> file.
<A NAME="IDX1204"></A>
<CODE>pnm:type-dimensions</CODE> returns a list of 4 items:
<OL>
<LI>
A symbol describing the type of the file named by <VAR>path</VAR>.
<LI>
The image width in pixels.
<LI>
The image height in pixels.
<LI>
The maximum value of pixels assume in the file.
</OL>
<P>
The current set of file-type symbols is:
</P>
<DL COMPACT>
<DT>pbm
<DD><DT>pbm-raw
<DD><A NAME="IDX1205"></A>
<A NAME="IDX1206"></A>
Black-and-White image; pixel values are 0 or 1.
<DT>pgm
<DD><DT>pgm-raw
<DD><A NAME="IDX1207"></A>
<A NAME="IDX1208"></A>
Gray (monochrome) image; pixel values are from 0 to <VAR>maxval</VAR>
specified in file header.
<DT>ppm
<DD><DT>ppm-raw
<DD><A NAME="IDX1209"></A>
<A NAME="IDX1210"></A>
RGB (full color) image; red, green, and blue interleaved pixel values
are from 0 to <VAR>maxval</VAR>
</DL>
</DL>
<P>
<A NAME="IDX1211"></A>
</P>
<DL>
<DT><U>Function:</U> <B>pnm:image-file->array</B> <I>path array</I>
<DD><P>
Reads the <EM>portable bitmap graphics</EM> file named by <VAR>path</VAR> into
<A NAME="IDX1212"></A>
<VAR>array</VAR>. <VAR>array</VAR> must be the correct size and type for
<VAR>path</VAR>. <VAR>array</VAR> is returned.
</P>
<P>
<A NAME="IDX1213"></A>
<DT><U>Function:</U> <B>pnm:image-file->array</B> <I>path</I>
<DD></P>
<P>
<CODE>pnm:image-file->array</CODE> creates and returns an array with the
<EM>portable bitmap graphics</EM> file named by <VAR>path</VAR> read into it.
<A NAME="IDX1214"></A>
</P>
</DL>
<P>
<A NAME="IDX1215"></A>
</P>
<DL>
<DT><U>Function:</U> <B>pnm:array-write</B> <I>type array maxval path comment <small>...</small></I>
<DD><P>
Writes the contents of <VAR>array</VAR> to a <VAR>type</VAR> image file named <VAR>path</VAR>. The file
will have pixel values between 0 and <VAR>maxval</VAR>, which must be compatible
with <VAR>type</VAR>. For `<SAMP>pbm</SAMP>' files, <VAR>maxval</VAR> must be `<SAMP>1</SAMP>'.
<VAR>comment</VAR>s are included in the file header.
</P>
</DL>
<P>
<A NAME="Collections"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.1.9 Collections </H3>
<!--docid::SEC194::-->
<P>
<CODE>(require 'collect)</CODE>
<A NAME="IDX1216"></A>
</P>
<P>
Routines for managing collections. Collections are aggregate data
structures supporting iteration over their elements, similar to the
Dylan(TM) language, but with a different interface. They have
<EM>elements</EM> indexed by corresponding <EM>keys</EM>, although the keys
may be implicit (as with lists).
</P>
<P>
New types of collections may be defined as YASOS objects (see section <A HREF="slib_3.html#SEC40">3.8 Yasos</A>).
They must support the following operations:
</P>
<P>
<UL>
<LI>
<CODE>(collection? <VAR>self</VAR>)</CODE> (always returns <CODE>#t</CODE>);
<P>
</P>
<LI>
<CODE>(size <VAR>self</VAR>)</CODE> returns the number of elements in the collection;
<P>
</P>
<LI>
<CODE>(print <VAR>self</VAR> <VAR>port</VAR>)</CODE> is a specialized print operation
for the collection which prints a suitable representation on the given
<VAR>port</VAR> or returns it as a string if <VAR>port</VAR> is <CODE>#t</CODE>;
<P>
</P>
<LI>
<A NAME="IDX1217"></A>
<CODE>(gen-elts <VAR>self</VAR>)</CODE> returns a thunk which on successive
invocations yields elements of <VAR>self</VAR> in order or gives an error if
it is invoked more than <CODE>(size <VAR>self</VAR>)</CODE> times;
<P>
</P>
<LI>
<A NAME="IDX1218"></A>
<CODE>(gen-keys <VAR>self</VAR>)</CODE> is like <CODE>gen-elts</CODE>, but yields the
collection's keys in order.
</UL>
<P>
They might support specialized <CODE>for-each-key</CODE> and
<CODE>for-each-elt</CODE> operations.
</P>
<P>
<A NAME="IDX1219"></A>
</P>
<DL>
<DT><U>Function:</U> <B>collection?</B> <I>obj</I>
<DD>A predicate, true initially of lists, vectors and strings. New sorts of
collections must answer <CODE>#t</CODE> to <CODE>collection?</CODE>.
</DL>
<P>
<A NAME="IDX1220"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>map-elts</B> <I>proc collection1 <small>...</small></I>
<DD><A NAME="IDX1221"></A>
<DT><U>Procedure:</U> <B>do-elts</B> <I>proc collection1 <small>...</small></I>
<DD><VAR>proc</VAR> is a procedure taking as many arguments as there are
<VAR>collections</VAR> (at least one). The <VAR>collections</VAR> are iterated
over in their natural order and <VAR>proc</VAR> is applied to the elements
yielded by each iteration in turn. The order in which the arguments are
supplied corresponds to te order in which the <VAR>collections</VAR> appear.
<CODE>do-elts</CODE> is used when only side-effects of <VAR>proc</VAR> are of
interest and its return value is unspecified. <CODE>map-elts</CODE> returns a
collection (actually a vector) of the results of the applications of
<VAR>proc</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(map-elts + (list 1 2 3) (vector 1 2 3))
=> #(2 4 6)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1222"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>map-keys</B> <I>proc collection1 <small>...</small></I>
<DD><A NAME="IDX1223"></A>
<DT><U>Procedure:</U> <B>do-keys</B> <I>proc collection1 <small>...</small></I>
<DD>These are analogous to <CODE>map-elts</CODE> and <CODE>do-elts</CODE>, but each
iteration is over the <VAR>collections</VAR>' <EM>keys</EM> rather than their
elements.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(map-keys + (list 1 2 3) (vector 1 2 3))
=> #(0 2 4)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1224"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>for-each-key</B> <I>collection proc</I>
<DD><A NAME="IDX1225"></A>
<DT><U>Procedure:</U> <B>for-each-elt</B> <I>collection proc</I>
<DD>These are like <CODE>do-keys</CODE> and <CODE>do-elts</CODE> but only for a single
collection; they are potentially more efficient.
</DL>
<P>
<A NAME="IDX1226"></A>
</P>
<DL>
<DT><U>Function:</U> <B>reduce</B> <I>proc seed collection1 <small>...</small></I>
<DD>A generalization of the list-based <CODE>reduce-init</CODE>
(see section <A HREF="slib_7.html#SEC211">7.2.1.3 Lists as sequences</A>) to collections which will shadow the
list-based version if <CODE>(require 'collect)</CODE> follows
<A NAME="IDX1227"></A>
<CODE>(require 'common-list-functions)</CODE> (see section <A HREF="slib_7.html#SEC208">7.2.1 Common List Functions</A>).
<A NAME="IDX1228"></A>
<P>
Examples:
<TABLE><tr><td> </td><td class=example><pre>(reduce + 0 (vector 1 2 3))
=> 6
(reduce union '() '((a b c) (b c d) (d a)))
=> (c b d a).
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1229"></A>
</P>
<DL>
<DT><U>Function:</U> <B>any?</B> <I>pred collection1 <small>...</small></I>
<DD>A generalization of the list-based <CODE>some</CODE> (see section <A HREF="slib_7.html#SEC211">7.2.1.3 Lists as sequences</A>) to collections.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(any? odd? (list 2 3 4 5))
=> #t
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1230"></A>
</P>
<DL>
<DT><U>Function:</U> <B>every?</B> <I>pred collection1 <small>...</small></I>
<DD>A generalization of the list-based <CODE>every</CODE>
(see section <A HREF="slib_7.html#SEC211">7.2.1.3 Lists as sequences</A>) to collections.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(every? collection? '((1 2) #(1 2)))
=> #t
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1231"></A>
</P>
<DL>
<DT><U>Function:</U> <B>empty?</B> <I>collection</I>
<DD>Returns <CODE>#t</CODE> iff there are no elements in <VAR>collection</VAR>.
<P>
<CODE>(empty? <VAR>collection</VAR>) == (zero? (size <VAR>collection</VAR>))</CODE>
</P>
</DL>
<P>
<A NAME="IDX1232"></A>
</P>
<DL>
<DT><U>Function:</U> <B>size</B> <I>collection</I>
<DD>Returns the number of elements in <VAR>collection</VAR>.
</DL>
<P>
<A NAME="IDX1233"></A>
</P>
<DL>
<DT><U>Function:</U> <B>Setter</B> <I>list-ref</I>
<DD>See <A HREF="slib_3.html#SEC43">3.8.3 Setters</A> for a definition of <EM>setter</EM>. N.B.
<CODE>(setter list-ref)</CODE> doesn't work properly for element 0 of a
list.
</DL>
<P>
Here is a sample collection: <CODE>simple-table</CODE> which is also a
<CODE>table</CODE>.
<TABLE><tr><td> </td><td class=example><pre>(define-predicate TABLE?)
(define-operation (LOOKUP table key failure-object))
(define-operation (ASSOCIATE! table key value)) ;; returns key
(define-operation (REMOVE! table key)) ;; returns value
(define (MAKE-SIMPLE-TABLE)
(let ( (table (list)) )
(object
;; table behaviors
((TABLE? self) #t)
((SIZE self) (size table))
((PRINT self port) (format port "#<SIMPLE-TABLE>"))
((LOOKUP self key failure-object)
(cond
((assq key table) => cdr)
(else failure-object)
))
((ASSOCIATE! self key value)
(cond
((assq key table)
=> (lambda (bucket) (set-cdr! bucket value) key))
(else
(set! table (cons (cons key value) table))
key)
))
((REMOVE! self key);; returns old value
(cond
((null? table) (slib:error "TABLE:REMOVE! Key not found: " key))
((eq? key (caar table))
(let ( (value (cdar table)) )
(set! table (cdr table))
value)
)
(else
(let loop ( (last table) (this (cdr table)) )
(cond
((null? this)
(slib:error "TABLE:REMOVE! Key not found: " key))
((eq? key (caar this))
(let ( (value (cdar this)) )
(set-cdr! last (cdr this))
value)
)
(else
(loop (cdr last) (cdr this)))
) ) )
))
;; collection behaviors
((COLLECTION? self) #t)
((GEN-KEYS self) (collect:list-gen-elts (map car table)))
((GEN-ELTS self) (collect:list-gen-elts (map cdr table)))
((FOR-EACH-KEY self proc)
(for-each (lambda (bucket) (proc (car bucket))) table)
)
((FOR-EACH-ELT self proc)
(for-each (lambda (bucket) (proc (cdr bucket))) table)
) ) ) )
</pre></td></tr></table><P>
<A NAME="Dynamic Data Type"></A>
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</TR></TABLE>
<H3> 7.1.10 Dynamic Data Type </H3>
<!--docid::SEC195::-->
<P>
<CODE>(require 'dynamic)</CODE>
<A NAME="IDX1234"></A>
</P>
<P>
<A NAME="IDX1235"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-dynamic</B> <I>obj</I>
<DD>Create and returns a new <EM>dynamic</EM> whose global value is <VAR>obj</VAR>.
</DL>
<P>
<A NAME="IDX1236"></A>
</P>
<DL>
<DT><U>Function:</U> <B>dynamic?</B> <I>obj</I>
<DD>Returns true if and only if <VAR>obj</VAR> is a dynamic. No object
satisfying <CODE>dynamic?</CODE> satisfies any of the other standard type
predicates.
</DL>
<P>
<A NAME="IDX1237"></A>
</P>
<DL>
<DT><U>Function:</U> <B>dynamic-ref</B> <I>dyn</I>
<DD>Return the value of the given dynamic in the current dynamic
environment.
</DL>
<P>
<A NAME="IDX1238"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>dynamic-set!</B> <I>dyn obj</I>
<DD>Change the value of the given dynamic to <VAR>obj</VAR> in the current
dynamic environment. The returned value is unspecified.
</DL>
<P>
<A NAME="IDX1239"></A>
</P>
<DL>
<DT><U>Function:</U> <B>call-with-dynamic-binding</B> <I>dyn obj thunk</I>
<DD>Invoke and return the value of the given thunk in a new, nested dynamic
environment in which the given dynamic has been bound to a new location
whose initial contents are the value <VAR>obj</VAR>. This dynamic
environment has precisely the same extent as the invocation of the thunk
and is thus captured by continuations created within that invocation and
re-established by those continuations when they are invoked.
</DL>
<P>
The <CODE>dynamic-bind</CODE> macro is not implemented.
</P>
<P>
<A NAME="Hash Tables"></A>
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</TR></TABLE>
<H3> 7.1.11 Hash Tables </H3>
<!--docid::SEC196::-->
<P>
<CODE>(require 'hash-table)</CODE>
<A NAME="IDX1240"></A>
</P>
<P>
<A NAME="IDX1241"></A>
</P>
<DL>
<DT><U>Function:</U> <B>predicate->hash</B> <I>pred</I>
<DD><P>
Returns a hash function (like <CODE>hashq</CODE>, <CODE>hashv</CODE>, or
<CODE>hash</CODE>) corresponding to the equality predicate <VAR>pred</VAR>.
<VAR>pred</VAR> should be <CODE>eq?</CODE>, <CODE>eqv?</CODE>, <CODE>equal?</CODE>, <CODE>=</CODE>,
<CODE>char=?</CODE>, <CODE>char-ci=?</CODE>, <CODE>string=?</CODE>, or
<CODE>string-ci=?</CODE>.
</P>
</DL>
A hash table is a vector of association lists.
<P>
<A NAME="IDX1242"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-hash-table</B> <I>k</I>
<DD><P>
Returns a vector of <VAR>k</VAR> empty (association) lists.
</P>
</DL>
Hash table functions provide utilities for an associative database.
These functions take an equality predicate, <VAR>pred</VAR>, as an argument.
<VAR>pred</VAR> should be <CODE>eq?</CODE>, <CODE>eqv?</CODE>, <CODE>equal?</CODE>, <CODE>=</CODE>,
<CODE>char=?</CODE>, <CODE>char-ci=?</CODE>, <CODE>string=?</CODE>, or
<CODE>string-ci=?</CODE>.
<P>
<A NAME="IDX1243"></A>
</P>
<DL>
<DT><U>Function:</U> <B>predicate->hash-asso</B> <I>pred</I>
<DD><P>
Returns a hash association function of 2 arguments, <VAR>key</VAR> and
<VAR>hashtab</VAR>, corresponding to <VAR>pred</VAR>. The returned function
returns a key-value pair whose key is <VAR>pred</VAR>-equal to its first
argument or <CODE>#f</CODE> if no key in <VAR>hashtab</VAR> is <VAR>pred</VAR>-equal to
the first argument.
</P>
</DL>
<P>
<A NAME="IDX1244"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hash-inquirer</B> <I>pred</I>
<DD><P>
Returns a procedure of 2 arguments, <VAR>hashtab</VAR> and <VAR>key</VAR>, which
returns the value associated with <VAR>key</VAR> in <VAR>hashtab</VAR> or
<CODE>#f</CODE> if <VAR>key</VAR> does not appear in <VAR>hashtab</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1245"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hash-associator</B> <I>pred</I>
<DD><P>
Returns a procedure of 3 arguments, <VAR>hashtab</VAR>, <VAR>key</VAR>, and
<VAR>value</VAR>, which modifies <VAR>hashtab</VAR> so that <VAR>key</VAR> and
<VAR>value</VAR> associated. Any previous value associated with <VAR>key</VAR>
will be lost.
</P>
</DL>
<P>
<A NAME="IDX1246"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hash-remover</B> <I>pred</I>
<DD><P>
Returns a procedure of 2 arguments, <VAR>hashtab</VAR> and <VAR>key</VAR>, which
modifies <VAR>hashtab</VAR> so that the association whose key is <VAR>key</VAR> is
removed.
</P>
</DL>
<P>
<A NAME="IDX1247"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hash-map</B> <I>proc hash-table</I>
<DD><P>
Returns a new hash table formed by mapping <VAR>proc</VAR> over the
keys and values of <VAR>hash-table</VAR>. <VAR>proc</VAR> must be a function of 2
arguments which returns the new value part.
</P>
</DL>
<P>
<A NAME="IDX1248"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hash-for-each</B> <I>proc hash-table</I>
<DD><P>
Applies <VAR>proc</VAR> to each pair of keys and values of <VAR>hash-table</VAR>.
<VAR>proc</VAR> must be a function of 2 arguments. The returned value is
unspecified.
</P>
</DL>
<P>
<A NAME="IDX1249"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hash-rehasher</B> <I>pred</I>
<DD><P>
<CODE>hash-rehasher</CODE> accepts a hash table predicate and returns a function of two
arguments <VAR>hashtab</VAR> and <VAR>new-k</VAR> which is specialized for
that predicate.
</P>
<P>
This function is used for nondestrutively resizing a hash table.
<VAR>hashtab</VAR> should be an existing hash-table using <VAR>pred</VAR>, <VAR>new-k</VAR>
is the size of a new hash table to be returned. The new hash table
will have all of the associations of the old hash table.
</P>
</DL>
<P>
<A NAME="Object"></A>
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<H3> 7.1.12 Macroless Object System </H3>
<!--docid::SEC197::-->
<P>
<CODE>(require 'object)</CODE>
<A NAME="IDX1250"></A>
</P>
<P>
This is the Macroless Object System written by Wade Humeniuk
(whumeniu@datap.ca). Conceptual Tributes: <A HREF="slib_3.html#SEC40">3.8 Yasos</A>, MacScheme's
%object, CLOS, Lack of R4RS macros.
</P>
<P>
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<H3> 7.1.13 Concepts </H3>
<!--docid::SEC198::-->
<DL COMPACT>
<DT>OBJECT
<DD>An object is an ordered association-list (by <CODE>eq?</CODE>) of methods
(procedures). Methods can be added (<CODE>make-method!</CODE>), deleted
(<CODE>unmake-method!</CODE>) and retrieved (<CODE>get-method</CODE>). Objects may
inherit methods from other objects. The object binds to the environment
it was created in, allowing closures to be used to hide private
procedures and data.
<P>
</P>
<DT>GENERIC-METHOD
<DD>A generic-method associates (in terms of <CODE>eq?</CODE>) object's method.
This allows scheme function style to be used for objects. The calling
scheme for using a generic method is <CODE>(generic-method object param1
param2 ...)</CODE>.
<P>
</P>
<DT>METHOD
<DD>A method is a procedure that exists in the object. To use a method
get-method must be called to look-up the method. Generic methods
implement the get-method functionality. Methods may be added to an
object associated with any scheme obj in terms of eq?
<P>
</P>
<DT>GENERIC-PREDICATE
<DD>A generic method that returns a boolean value for any scheme obj.
<P>
</P>
<DT>PREDICATE
<DD>A object's method asscociated with a generic-predicate. Returns
<CODE>#t</CODE>.
</DL>
<P>
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<H3> 7.1.14 Procedures </H3>
<!--docid::SEC199::-->
<P>
<A NAME="IDX1251"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-object</B> <I>ancestor <small>...</small></I>
<DD>Returns an object. Current object implementation is a tagged vector.
<VAR>ancestor</VAR>s are optional and must be objects in terms of object?.
<VAR>ancestor</VAR>s methods are included in the object. Multiple
<VAR>ancestor</VAR>s might associate the same generic-method with a method.
In this case the method of the <VAR>ancestor</VAR> first appearing in the
list is the one returned by <CODE>get-method</CODE>.
</DL>
<P>
<A NAME="IDX1252"></A>
</P>
<DL>
<DT><U>Function:</U> <B>object?</B> <I>obj</I>
<DD>Returns boolean value whether <VAR>obj</VAR> was created by make-object.
</DL>
<P>
<A NAME="IDX1253"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-generic-method</B> <I>exception-procedure</I>
<DD>Returns a procedure which be associated with an object's methods. If
<VAR>exception-procedure</VAR> is specified then it is used to process
non-objects.
</DL>
<P>
<A NAME="IDX1254"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-generic-predicate</B>
<DD>Returns a boolean procedure for any scheme object.
</DL>
<P>
<A NAME="IDX1255"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-method!</B> <I>object generic-method method</I>
<DD>Associates <VAR>method</VAR> to the <VAR>generic-method</VAR> in the object. The
<VAR>method</VAR> overrides any previous association with the
<VAR>generic-method</VAR> within the object. Using <CODE>unmake-method!</CODE>
will restore the object's previous association with the
<VAR>generic-method</VAR>. <VAR>method</VAR> must be a procedure.
</DL>
<P>
<A NAME="IDX1256"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-predicate!</B> <I>object generic-preciate</I>
<DD>Makes a predicate method associated with the <VAR>generic-predicate</VAR>.
</DL>
<P>
<A NAME="IDX1257"></A>
</P>
<DL>
<DT><U>Function:</U> <B>unmake-method!</B> <I>object generic-method</I>
<DD>Removes an object's association with a <VAR>generic-method</VAR> .
</DL>
<P>
<A NAME="IDX1258"></A>
</P>
<DL>
<DT><U>Function:</U> <B>get-method</B> <I>object generic-method</I>
<DD>Returns the object's method associated (if any) with the
<VAR>generic-method</VAR>. If no associated method exists an error is
flagged.
</DL>
<P>
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<H3> 7.1.15 Examples </H3>
<!--docid::SEC200::-->
<P>
<TABLE><tr><td> </td><td class=example><pre>(require 'object)
<A NAME="IDX1259"></A>
(define instantiate (make-generic-method))
(define (make-instance-object . ancestors)
(define self (apply make-object
(map (lambda (obj) (instantiate obj)) ancestors)))
(make-method! self instantiate (lambda (self) self))
self)
(define who (make-generic-method))
(define imigrate! (make-generic-method))
(define emigrate! (make-generic-method))
(define describe (make-generic-method))
(define name (make-generic-method))
(define address (make-generic-method))
(define members (make-generic-method))
(define society
(let ()
(define self (make-instance-object))
(define population '())
(make-method! self imigrate!
(lambda (new-person)
(if (not (eq? new-person self))
(set! population (cons new-person population)))))
(make-method! self emigrate!
(lambda (person)
(if (not (eq? person self))
(set! population
(comlist:remove-if (lambda (member)
(eq? member person))
population)))))
(make-method! self describe
(lambda (self)
(map (lambda (person) (describe person)) population)))
(make-method! self who
(lambda (self) (map (lambda (person) (name person))
population)))
(make-method! self members (lambda (self) population))
self))
(define (make-person %name %address)
(define self (make-instance-object society))
(make-method! self name (lambda (self) %name))
(make-method! self address (lambda (self) %address))
(make-method! self who (lambda (self) (name self)))
(make-method! self instantiate
(lambda (self)
(make-person (string-append (name self) "-son-of")
%address)))
(make-method! self describe
(lambda (self) (list (name self) (address self))))
(imigrate! self)
self)
</pre></td></tr></table><P>
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<H4> 7.1.15.1 Inverter Documentation </H4>
<!--docid::SEC201::-->
Inheritance:
<TABLE><tr><td> </td><td class=example><pre> <inverter>::(<number> <description>)
</pre></td></tr></table>Generic-methods
<TABLE><tr><td> </td><td class=example><pre> <inverter>::value => <number>::value
<inverter>::set-value! => <number>::set-value!
<inverter>::describe => <description>::describe
<inverter>::help
<inverter>::invert
<inverter>::inverter?
</pre></td></tr></table><P>
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<H4> 7.1.15.2 Number Documention </H4>
<!--docid::SEC202::-->
Inheritance
<TABLE><tr><td> </td><td class=example><pre> <number>::()
</pre></td></tr></table>Slots
<TABLE><tr><td> </td><td class=example><pre> <number>::<x>
</pre></td></tr></table>Generic Methods
<TABLE><tr><td> </td><td class=example><pre> <number>::value
<number>::set-value!
</pre></td></tr></table><P>
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<H4> 7.1.15.3 Inverter code </H4>
<!--docid::SEC203::-->
<TABLE><tr><td> </td><td class=example><pre>(require 'object)
<A NAME="IDX1260"></A>
(define value (make-generic-method (lambda (val) val)))
(define set-value! (make-generic-method))
(define invert (make-generic-method
(lambda (val)
(if (number? val)
(/ 1 val)
(error "Method not supported:" val)))))
(define noop (make-generic-method))
(define inverter? (make-generic-predicate))
(define describe (make-generic-method))
(define help (make-generic-method))
(define (make-number x)
(define self (make-object))
(make-method! self value (lambda (this) x))
(make-method! self set-value!
(lambda (this new-value) (set! x new-value)))
self)
(define (make-description str)
(define self (make-object))
(make-method! self describe (lambda (this) str))
(make-method! self help (lambda (this) "Help not available"))
self)
(define (make-inverter)
(let* ((self (make-object
(make-number 1)
(make-description "A number which can be inverted")))
(<value> (get-method self value)))
(make-method! self invert (lambda (self) (/ 1 (<value> self))))
(make-predicate! self inverter?)
(unmake-method! self help)
(make-method! self help
(lambda (self)
(display "Inverter Methods:") (newline)
(display " (value inverter) ==> n") (newline)))
self))
;;;; Try it out
(define invert! (make-generic-method))
(define x (make-inverter))
(make-method! x invert! (lambda (x) (set-value! x (/ 1 (value x)))))
(value x) => 1
(set-value! x 33) => undefined
(invert! x) => undefined
(value x) => 1/33
(unmake-method! x invert!) => undefined
(invert! x) error--> ERROR: Method not supported: x
</pre></td></tr></table><P>
<A NAME="Priority Queues"></A>
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<H3> 7.1.16 Priority Queues </H3>
<!--docid::SEC204::-->
<P>
<CODE>(require 'priority-queue)</CODE>
<A NAME="IDX1261"></A>
</P>
<P>
This algorithm for priority queues is due to
<CITE>Introduction to Algorithms</CITE>
by T. Cormen, C. Leiserson, R. Rivest.
1989 MIT Press.
</P>
<P>
<A NAME="IDX1262"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-heap</B> <I>pred<?</I>
<DD><P>
Returns a binary heap suitable which can be used for priority queue
operations.
</P>
</DL>
<P>
<A NAME="IDX1263"></A>
</P>
<DL>
<DT><U>Function:</U> <B>heap-length</B> <I>heap</I>
<DD><P>
Returns the number of elements in <VAR>heap</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1264"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>heap-insert!</B> <I>heap item</I>
<DD><P>
Inserts <VAR>item</VAR> into <VAR>heap</VAR>. <VAR>item</VAR> can be inserted multiple
times. The value returned is unspecified.
</P>
</DL>
<P>
<A NAME="IDX1265"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>heap-extract-max!</B> <I>heap</I>
<DD><P>
Returns the item which is larger than all others according to the
<VAR>pred<?</VAR> argument to <CODE>make-heap</CODE>. If there are no items in
<VAR>heap</VAR>, an error is signaled.
</P>
</DL>
<P>
<A NAME="Queues"></A>
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<H3> 7.1.17 Queues </H3>
<!--docid::SEC205::-->
<P>
<CODE>(require 'queue)</CODE>
<A NAME="IDX1266"></A>
</P>
<P>
A <EM>queue</EM> is a list where elements can be added to both the front
<A NAME="IDX1267"></A>
and rear, and removed from the front (i.e., they are what are often
called <EM>dequeues</EM>). A queue may also be used like a stack.
<A NAME="IDX1268"></A>
</P>
<P>
<A NAME="IDX1269"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-queue</B>
<DD><P>
Returns a new, empty queue.
</P>
</DL>
<P>
<A NAME="IDX1270"></A>
</P>
<DL>
<DT><U>Function:</U> <B>queue?</B> <I>obj</I>
<DD><P>
Returns <CODE>#t</CODE> if <VAR>obj</VAR> is a queue.
</P>
</DL>
<P>
<A NAME="IDX1271"></A>
</P>
<DL>
<DT><U>Function:</U> <B>queue-empty?</B> <I>q</I>
<DD><P>
Returns <CODE>#t</CODE> if the queue <VAR>q</VAR> is empty.
</P>
</DL>
<P>
<A NAME="IDX1272"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>queue-push!</B> <I>q datum</I>
<DD><P>
Adds <VAR>datum</VAR> to the front of queue <VAR>q</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1273"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>enqueue!</B> <I>q datum</I>
<DD><P>
Adds <VAR>datum</VAR> to the rear of queue <VAR>q</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1274"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>dequeue!</B> <I>q</I>
<DD><P>
<A NAME="IDX1275"></A>
<DT><U>Procedure:</U> <B>queue-pop!</B> <I>q</I>
<DD>Both of these procedures remove and return the datum at the front of
the queue. <CODE>queue-pop!</CODE> is used to suggest that the queue is
being used like a stack.
</P>
</DL>
All of the following functions raise an error if the queue <VAR>q</VAR>
is empty.
<P>
<A NAME="IDX1276"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>dequeue-all!</B> <I>q</I>
<DD><P>
Removes and returns (the list) of all contents of queue <VAR>q</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1277"></A>
</P>
<DL>
<DT><U>Function:</U> <B>queue-front</B> <I>q</I>
<DD><P>
Returns the datum at the front of the queue <VAR>q</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1278"></A>
</P>
<DL>
<DT><U>Function:</U> <B>queue-rear</B> <I>q</I>
<DD><P>
Returns the datum at the rear of the queue <VAR>q</VAR>.
</P>
</DL>
<P>
<A NAME="Records"></A>
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<H3> 7.1.18 Records </H3>
<!--docid::SEC206::-->
<P>
<CODE>(require 'record)</CODE>
<A NAME="IDX1279"></A>
</P>
<P>
The Record package provides a facility for user to define their own
record data types.
</P>
<P>
<A NAME="IDX1280"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-record-type</B> <I>type-name field-names</I>
<DD>Returns a <EM>record-type descriptor</EM>, a value representing a new data
type disjoint from all others. The <VAR>type-name</VAR> argument must be a
string, but is only used for debugging purposes (such as the printed
representation of a record of the new type). The <VAR>field-names</VAR>
argument is a list of symbols naming the <EM>fields</EM> of a record of the
new type. It is an error if the list contains any duplicates. It is
unspecified how record-type descriptors are represented.
</DL>
<P>
<A NAME="IDX1281"></A>
</P>
<DL>
<DT><U>Function:</U> <B>record-constructor</B> <I>rtd [field-names]</I>
<DD>Returns a procedure for constructing new members of the type represented
by <VAR>rtd</VAR>. The returned procedure accepts exactly as many arguments
as there are symbols in the given list, <VAR>field-names</VAR>; these are
used, in order, as the initial values of those fields in a new record,
which is returned by the constructor procedure. The values of any
fields not named in that list are unspecified. The <VAR>field-names</VAR>
argument defaults to the list of field names in the call to
<CODE>make-record-type</CODE> that created the type represented by <VAR>rtd</VAR>;
if the <VAR>field-names</VAR> argument is provided, it is an error if it
contains any duplicates or any symbols not in the default list.
</DL>
<P>
<A NAME="IDX1282"></A>
</P>
<DL>
<DT><U>Function:</U> <B>record-predicate</B> <I>rtd</I>
<DD>Returns a procedure for testing membership in the type represented by
<VAR>rtd</VAR>. The returned procedure accepts exactly one argument and
returns a true value if the argument is a member of the indicated record
type; it returns a false value otherwise.
</DL>
<P>
<A NAME="IDX1283"></A>
</P>
<DL>
<DT><U>Function:</U> <B>record-accessor</B> <I>rtd field-name</I>
<DD>Returns a procedure for reading the value of a particular field of a
member of the type represented by <VAR>rtd</VAR>. The returned procedure
accepts exactly one argument which must be a record of the appropriate
type; it returns the current value of the field named by the symbol
<VAR>field-name</VAR> in that record. The symbol <VAR>field-name</VAR> must be a
member of the list of field-names in the call to <CODE>make-record-type</CODE>
that created the type represented by <VAR>rtd</VAR>.
</DL>
<P>
<A NAME="IDX1284"></A>
</P>
<DL>
<DT><U>Function:</U> <B>record-modifier</B> <I>rtd field-name</I>
<DD>Returns a procedure for writing the value of a particular field of a
member of the type represented by <VAR>rtd</VAR>. The returned procedure
accepts exactly two arguments: first, a record of the appropriate type,
and second, an arbitrary Scheme value; it modifies the field named by
the symbol <VAR>field-name</VAR> in that record to contain the given value.
The returned value of the modifier procedure is unspecified. The symbol
<VAR>field-name</VAR> must be a member of the list of field-names in the call
to <CODE>make-record-type</CODE> that created the type represented by
<VAR>rtd</VAR>.
</DL>
<P>
In May of 1996, as a product of discussion on the <CODE>rrrs-authors</CODE>
mailing list, I rewrote `<TT>record.scm</TT>' to portably implement type
disjointness for record data types.
</P>
<P>
As long as an implementation's procedures are opaque and the
<CODE>record</CODE> code is loaded before other programs, this will give
disjoint record types which are unforgeable and incorruptible by R4RS
procedures.
</P>
<P>
As a consequence, the procedures <CODE>record?</CODE>,
<CODE>record-type-descriptor</CODE>, <CODE>record-type-name</CODE>.and
<CODE>record-type-field-names</CODE> are no longer supported.
</P>
<P>
<A NAME="Sorting and Searching"></A>
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<H2> 7.2 Sorting and Searching </H2>
<!--docid::SEC207::-->
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC208">7.2.1 Common List Functions</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'common-list-functions</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC214">7.2.2 Tree operations</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'tree</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC215">7.2.3 Chapter Ordering</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'chapter-order</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC216">7.2.4 Sorting</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'sort</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC217">7.2.5 Topological Sort</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Keep your socks on.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC218">7.2.6 Hashing</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'hash</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC219">7.2.7 Space-Filling Curves</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'hilbert and 'sierpinski</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC222">7.2.8 Soundex</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Dimension Reduction of Last Names</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC223">7.2.9 String Search</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Also Search from a Port.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC224">7.2.10 Sequence Comparison</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'diff and longest-common-subsequence</TD></TR>
</TABLE>
<P>
<A NAME="Common List Functions"></A>
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<H3> 7.2.1 Common List Functions </H3>
<!--docid::SEC208::-->
<P>
<CODE>(require 'common-list-functions)</CODE>
<A NAME="IDX1285"></A>
</P>
<P>
The procedures below follow the Common LISP equivalents apart from
optional arguments in some cases.
</P>
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC209">7.2.1.1 List construction</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC210">7.2.1.2 Lists as sets</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC211">7.2.1.3 Lists as sequences</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC212">7.2.1.4 Destructive list operations</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC213">7.2.1.5 Non-List functions</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
</TABLE>
<P>
<A NAME="List construction"></A>
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</TR></TABLE>
<H4> 7.2.1.1 List construction </H4>
<!--docid::SEC209::-->
<P>
<A NAME="IDX1286"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-list</B> <I>k</I>
<DD><A NAME="IDX1287"></A>
<DT><U>Function:</U> <B>make-list</B> <I>k init</I>
<DD><CODE>make-list</CODE> creates and returns a list of <VAR>k</VAR> elements. If
<VAR>init</VAR> is included, all elements in the list are initialized to
<VAR>init</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(make-list 3)
=> (#<unspecified> #<unspecified> #<unspecified>)
(make-list 5 'foo)
=> (foo foo foo foo foo)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1288"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list*</B> <I>obj1 obj2 <small>...</small></I>
<DD>Works like <CODE>list</CODE> except that the cdr of the last pair is the last
argument unless there is only one argument, when the result is just that
argument. Sometimes called <CODE>cons*</CODE>. E.g.:
<P>
<TABLE><tr><td> </td><td class=example><pre>(list* 1)
=> 1
(list* 1 2 3)
=> (1 2 . 3)
(list* 1 2 '(3 4))
=> (1 2 3 4)
(list* <VAR>args</VAR> '())
== (list <VAR>args</VAR>)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1289"></A>
</P>
<DL>
<DT><U>Function:</U> <B>copy-list</B> <I>lst</I>
<DD><CODE>copy-list</CODE> makes a copy of <VAR>lst</VAR> using new pairs and returns
it. Only the top level of the list is copied, i.e., pairs forming
elements of the copied list remain <CODE>eq?</CODE> to the corresponding
elements of the original; the copy is, however, not <CODE>eq?</CODE> to the
original, but is <CODE>equal?</CODE> to it.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(copy-list '(foo foo foo))
=> (foo foo foo)
(define q '(foo bar baz bang))
(define p q)
(eq? p q)
=> #t
(define r (copy-list q))
(eq? q r)
=> #f
(equal? q r)
=> #t
(define bar '(bar))
(eq? bar (car (copy-list (list bar 'foo))))
=> #t
</pre></td></tr></table></DL>
<P>
<A NAME="Lists as sets"></A>
<HR SIZE="6">
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</TR></TABLE>
<H4> 7.2.1.2 Lists as sets </H4>
<!--docid::SEC210::-->
<P>
<CODE>eqv?</CODE> is used to test for membership by procedures which treat
lists as sets.
</P>
<P>
<A NAME="IDX1290"></A>
</P>
<DL>
<DT><U>Function:</U> <B>adjoin</B> <I>e l</I>
<DD><CODE>adjoin</CODE> returns the adjoint of the element <VAR>e</VAR> and the list
<VAR>l</VAR>. That is, if <VAR>e</VAR> is in <VAR>l</VAR>, <CODE>adjoin</CODE> returns
<VAR>l</VAR>, otherwise, it returns <CODE>(cons <VAR>e</VAR> <VAR>l</VAR>)</CODE>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(adjoin 'baz '(bar baz bang))
=> (bar baz bang)
(adjoin 'foo '(bar baz bang))
=> (foo bar baz bang)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1291"></A>
</P>
<DL>
<DT><U>Function:</U> <B>union</B> <I>l1 l2</I>
<DD><CODE>union</CODE> returns a list of all elements that are in <VAR>l1</VAR> or
<VAR>l2</VAR>. Duplicates between <VAR>l1</VAR> and <VAR>l2</VAR> are culled.
Duplicates within <VAR>l1</VAR> or within <VAR>l2</VAR> may or may not be
removed.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(union '(1 2 3 4) '(5 6 7 8))
=> (1 2 3 4 5 6 7 8)
(union '(0 1 2 3 4) '(3 4 5 6))
=> (5 6 0 1 2 3 4)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1292"></A>
</P>
<DL>
<DT><U>Function:</U> <B>intersection</B> <I>l1 l2</I>
<DD><CODE>intersection</CODE> returns a list of all elements that are in both
<VAR>l1</VAR> and <VAR>l2</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(intersection '(1 2 3 4) '(3 4 5 6))
=> (3 4)
(intersection '(1 2 3 4) '(5 6 7 8))
=> ()
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1293"></A>
</P>
<DL>
<DT><U>Function:</U> <B>set-difference</B> <I>l1 l2</I>
<DD><CODE>set-difference</CODE> returns a list of all elements that are in
<VAR>l1</VAR> but not in <VAR>l2</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(set-difference '(1 2 3 4) '(3 4 5 6))
=> (1 2)
(set-difference '(1 2 3 4) '(1 2 3 4 5 6))
=> ()
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1294"></A>
</P>
<DL>
<DT><U>Function:</U> <B>subset?</B> <I>list1 list2</I>
<DD>Returns <CODE>#t</CODE> if every element of <VAR>list1</VAR> is <CODE>eqv?</CODE> an
element of <VAR>list2</VAR>; otherwise returns <CODE>#f</CODE>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(subset? '(1 2 3 4) '(3 4 5 6))
=> #f
(subset? '(1 2 3 4) '(6 5 4 3 2 1 0))
=> #t
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1295"></A>
</P>
<DL>
<DT><U>Function:</U> <B>member-if</B> <I>pred lst</I>
<DD><CODE>member-if</CODE> returns the list headed by the first element of
<VAR>lst</VAR> to satisfy <CODE>(<VAR>pred</VAR> <VAR>element</VAR>)</CODE>.
<CODE>Member-if</CODE> returns <CODE>#f</CODE> if <VAR>pred</VAR> returns <CODE>#f</CODE> for
every <VAR>element</VAR> in <VAR>lst</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(member-if vector? '(a 2 b 4))
=> #f
(member-if number? '(a 2 b 4))
=> (2 b 4)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1296"></A>
</P>
<DL>
<DT><U>Function:</U> <B>some</B> <I>pred lst1 lst2 <small>...</small></I>
<DD><VAR>pred</VAR> is a boolean function of as many arguments as there are list
arguments to <CODE>some</CODE> i.e., <VAR>lst</VAR> plus any optional arguments.
<VAR>pred</VAR> is applied to successive elements of the list arguments in
order. <CODE>some</CODE> returns <CODE>#t</CODE> as soon as one of these
applications returns <CODE>#t</CODE>, and is <CODE>#f</CODE> if none returns
<CODE>#t</CODE>. All the lists should have the same length.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(some odd? '(1 2 3 4))
=> #t
(some odd? '(2 4 6 8))
=> #f
(some > '(1 3) '(2 4))
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1297"></A>
</P>
<DL>
<DT><U>Function:</U> <B>every</B> <I>pred lst1 lst2 <small>...</small></I>
<DD><CODE>every</CODE> is analogous to <CODE>some</CODE> except it returns <CODE>#t</CODE> if
every application of <VAR>pred</VAR> is <CODE>#t</CODE> and <CODE>#f</CODE>
otherwise.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(every even? '(1 2 3 4))
=> #f
(every even? '(2 4 6 8))
=> #t
(every > '(2 3) '(1 4))
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1298"></A>
</P>
<DL>
<DT><U>Function:</U> <B>notany</B> <I>pred lst1 <small>...</small></I>
<DD><CODE>notany</CODE> is analogous to <CODE>some</CODE> but returns <CODE>#t</CODE> if no
application of <VAR>pred</VAR> returns <CODE>#t</CODE> or <CODE>#f</CODE> as soon as any
one does.
</DL>
<P>
<A NAME="IDX1299"></A>
</P>
<DL>
<DT><U>Function:</U> <B>notevery</B> <I>pred lst1 <small>...</small></I>
<DD><CODE>notevery</CODE> is analogous to <CODE>some</CODE> but returns <CODE>#t</CODE> as soon
as an application of <VAR>pred</VAR> returns <CODE>#f</CODE>, and <CODE>#f</CODE>
otherwise.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(notevery even? '(1 2 3 4))
=> #t
(notevery even? '(2 4 6 8))
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1300"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list-of??</B> <I>predicate</I>
<DD>Returns a predicate which returns true if its argument is a list every
element of which satisfies <VAR>predicate</VAR>.
<P>
<A NAME="IDX1301"></A>
<DT><U>Function:</U> <B>list-of??</B> <I>predicate low-bound high-bound</I>
<DD><VAR>low-bound</VAR> and <VAR>high-bound</VAR> are non-negative integers.
<CODE>list-of??</CODE> returns a predicate which returns true if its argument
is a list of length between <VAR>low-bound</VAR> and <VAR>high-bound</VAR>
(inclusive); every element of which satisfies <VAR>predicate</VAR>.
</P>
<P>
<A NAME="IDX1302"></A>
<DT><U>Function:</U> <B>list-of??</B> <I>predicate bound</I>
<DD><VAR>bound</VAR> is an integer. If <VAR>bound</VAR> is negative, <CODE>list-of??</CODE>
returns a predicate which returns true if its argument is a list of
length greater than <CODE>(- <VAR>bound</VAR>)</CODE>; every element of which
satisfies <VAR>predicate</VAR>. Otherwise, <CODE>list-of??</CODE> returns a
predicate which returns true if its argument is a list of length less
than or equal to <VAR>bound</VAR>; every element of which satisfies
<VAR>predicate</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1303"></A>
</P>
<DL>
<DT><U>Function:</U> <B>find-if</B> <I>pred lst</I>
<DD><CODE>find-if</CODE> searches for the first <VAR>element</VAR> in <VAR>lst</VAR> such
that <CODE>(<VAR>pred</VAR> <VAR>element</VAR>)</CODE> returns <CODE>#t</CODE>. If it finds
any such <VAR>element</VAR> in <VAR>lst</VAR>, <VAR>element</VAR> is returned.
Otherwise, <CODE>#f</CODE> is returned.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(find-if number? '(foo 1 bar 2))
=> 1
(find-if number? '(foo bar baz bang))
=> #f
(find-if symbol? '(1 2 foo bar))
=> foo
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1304"></A>
</P>
<DL>
<DT><U>Function:</U> <B>remove</B> <I>elt lst</I>
<DD><CODE>remove</CODE> removes all occurrences of <VAR>elt</VAR> from <VAR>lst</VAR> using
<CODE>eqv?</CODE> to test for equality and returns everything that's left.
N.B.: other implementations (Chez, Scheme->C and T, at least) use
<CODE>equal?</CODE> as the equality test.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(remove 1 '(1 2 1 3 1 4 1 5))
=> (2 3 4 5)
(remove 'foo '(bar baz bang))
=> (bar baz bang)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1305"></A>
</P>
<DL>
<DT><U>Function:</U> <B>remove-if</B> <I>pred lst</I>
<DD><CODE>remove-if</CODE> removes all <VAR>element</VAR>s from <VAR>lst</VAR> where
<CODE>(<VAR>pred</VAR> <VAR>element</VAR>)</CODE> is <CODE>#t</CODE> and returns everything
that's left.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(remove-if number? '(1 2 3 4))
=> ()
(remove-if even? '(1 2 3 4 5 6 7 8))
=> (1 3 5 7)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1306"></A>
</P>
<DL>
<DT><U>Function:</U> <B>remove-if-not</B> <I>pred lst</I>
<DD><CODE>remove-if-not</CODE> removes all <VAR>element</VAR>s from <VAR>lst</VAR> for which
<CODE>(<VAR>pred</VAR> <VAR>element</VAR>)</CODE> is <CODE>#f</CODE> and returns everything that's
left.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(remove-if-not number? '(foo bar baz))
=> ()
(remove-if-not odd? '(1 2 3 4 5 6 7 8))
=> (1 3 5 7)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1307"></A>
</P>
<DL>
<DT><U>Function:</U> <B>has-duplicates?</B> <I>lst</I>
<DD>returns <CODE>#t</CODE> if 2 members of <VAR>lst</VAR> are <CODE>equal?</CODE>, <CODE>#f</CODE>
otherwise.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(has-duplicates? '(1 2 3 4))
=> #f
(has-duplicates? '(2 4 3 4))
=> #t
</pre></td></tr></table></DL>
<P>
The procedure <CODE>remove-duplicates</CODE> uses <CODE>member</CODE> (rather than
<CODE>memv</CODE>).
</P>
<P>
<A NAME="IDX1308"></A>
</P>
<DL>
<DT><U>Function:</U> <B>remove-duplicates</B> <I>lst</I>
<DD>returns a copy of <VAR>lst</VAR> with its duplicate members removed.
Elements are considered duplicate if they are <CODE>equal?</CODE>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(remove-duplicates '(1 2 3 4))
=> (1 2 3 4)
(remove-duplicates '(2 4 3 4))
=> (2 4 3)
</pre></td></tr></table></DL>
<P>
<A NAME="Lists as sequences"></A>
<HR SIZE="6">
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H4> 7.2.1.3 Lists as sequences </H4>
<!--docid::SEC211::-->
<P>
<A NAME="IDX1309"></A>
</P>
<DL>
<DT><U>Function:</U> <B>position</B> <I>obj lst</I>
<DD><CODE>position</CODE> returns the 0-based position of <VAR>obj</VAR> in <VAR>lst</VAR>,
or <CODE>#f</CODE> if <VAR>obj</VAR> does not occur in <VAR>lst</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(position 'foo '(foo bar baz bang))
=> 0
(position 'baz '(foo bar baz bang))
=> 2
(position 'oops '(foo bar baz bang))
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1310"></A>
</P>
<DL>
<DT><U>Function:</U> <B>reduce</B> <I>p lst</I>
<DD><CODE>reduce</CODE> combines all the elements of a sequence using a binary
operation (the combination is left-associative). For example, using
<CODE>+</CODE>, one can add up all the elements. <CODE>reduce</CODE> allows you to
apply a function which accepts only two arguments to more than 2
objects. Functional programmers usually refer to this as <EM>foldl</EM>.
<CODE>collect:reduce</CODE> (see section <A HREF="slib_7.html#SEC194">7.1.9 Collections</A>) provides a version of
<CODE>collect</CODE> generalized to collections.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(reduce + '(1 2 3 4))
=> 10
(define (bad-sum . l) (reduce + l))
(bad-sum 1 2 3 4)
== (reduce + (1 2 3 4))
== (+ (+ (+ 1 2) 3) 4)
=> 10
(bad-sum)
== (reduce + ())
=> ()
(reduce string-append '("hello" "cruel" "world"))
== (string-append (string-append "hello" "cruel") "world")
=> "hellocruelworld"
(reduce anything '())
=> ()
(reduce anything '(x))
=> x
</pre></td></tr></table><P>
What follows is a rather non-standard implementation of <CODE>reverse</CODE>
in terms of <CODE>reduce</CODE> and a combinator elsewhere called
<EM>C</EM>.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>;;; Contributed by Jussi Piitulainen (jpiitula @ ling.helsinki.fi)
(define commute
(lambda (f)
(lambda (x y)
(f y x))))
(define reverse
(lambda (args)
(reduce-init (commute cons) '() args)))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1311"></A>
</P>
<DL>
<DT><U>Function:</U> <B>reduce-init</B> <I>p init lst</I>
<DD><CODE>reduce-init</CODE> is the same as reduce, except that it implicitly
inserts <VAR>init</VAR> at the start of the list. <CODE>reduce-init</CODE> is
preferred if you want to handle the null list, the one-element, and
lists with two or more elements consistently. It is common to use the
operator's idempotent as the initializer. Functional programmers
usually call this <EM>foldl</EM>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(define (sum . l) (reduce-init + 0 l))
(sum 1 2 3 4)
== (reduce-init + 0 (1 2 3 4))
== (+ (+ (+ (+ 0 1) 2) 3) 4)
=> 10
(sum)
== (reduce-init + 0 '())
=> 0
(reduce-init string-append "@" '("hello" "cruel" "world"))
==
(string-append (string-append (string-append "@" "hello")
"cruel")
"world")
=> "@hellocruelworld"
</pre></td></tr></table><P>
Given a differentiation of 2 arguments, <CODE>diff</CODE>, the following will
differentiate by any number of variables.
<TABLE><tr><td> </td><td class=example><pre>(define (diff* exp . vars)
(reduce-init diff exp vars))
</pre></td></tr></table><P>
Example:
<TABLE><tr><td> </td><td class=example><pre>;;; Real-world example: Insertion sort using reduce-init.
(define (insert l item)
(if (null? l)
(list item)
(if (< (car l) item)
(cons (car l) (insert (cdr l) item))
(cons item l))))
(define (insertion-sort l) (reduce-init insert '() l))
(insertion-sort '(3 1 4 1 5)
== (reduce-init insert () (3 1 4 1 5))
== (insert (insert (insert (insert (insert () 3) 1) 4) 1) 5)
== (insert (insert (insert (insert (3)) 1) 4) 1) 5)
== (insert (insert (insert (1 3) 4) 1) 5)
== (insert (insert (1 3 4) 1) 5)
== (insert (1 1 3 4) 5)
=> (1 1 3 4 5)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1312"></A>
</P>
<DL>
<DT><U>Function:</U> <B>last</B> <I>lst n</I>
<DD><CODE>last</CODE> returns the last <VAR>n</VAR> elements of <VAR>lst</VAR>. <VAR>n</VAR>
must be a non-negative integer.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(last '(foo bar baz bang) 2)
=> (baz bang)
(last '(1 2 3) 0)
=> 0
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1313"></A>
</P>
<DL>
<DT><U>Function:</U> <B>butlast</B> <I>lst n</I>
<DD><CODE>butlast</CODE> returns all but the last <VAR>n</VAR> elements of
<VAR>lst</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(butlast '(a b c d) 3)
=> (a)
(butlast '(a b c d) 4)
=> ()
</pre></td></tr></table></DL>
<P>
<CODE>last</CODE> and <CODE>butlast</CODE> split a list into two parts when given
identical arugments.
<TABLE><tr><td> </td><td class=example><pre>(last '(a b c d e) 2)
=> (d e)
(butlast '(a b c d e) 2)
=> (a b c)
</pre></td></tr></table><P>
<A NAME="IDX1314"></A>
</P>
<DL>
<DT><U>Function:</U> <B>nthcdr</B> <I>n lst</I>
<DD><CODE>nthcdr</CODE> takes <VAR>n</VAR> <CODE>cdr</CODE>s of <VAR>lst</VAR> and returns the
result. Thus <CODE>(nthcdr 3 <VAR>lst</VAR>)</CODE> == <CODE>(cdddr
<VAR>lst</VAR>)</CODE>
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(nthcdr 2 '(a b c d))
=> (c d)
(nthcdr 0 '(a b c d))
=> (a b c d)
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1315"></A>
</P>
<DL>
<DT><U>Function:</U> <B>butnthcdr</B> <I>n lst</I>
<DD><CODE>butnthcdr</CODE> returns all but the nthcdr <VAR>n</VAR> elements of
<VAR>lst</VAR>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(butnthcdr 3 '(a b c d))
=> (a b c)
(butnthcdr 4 '(a b c d))
=> (a b c d)
</pre></td></tr></table></DL>
<P>
<CODE>nthcdr</CODE> and <CODE>butnthcdr</CODE> split a list into two parts when
given identical arugments.
<TABLE><tr><td> </td><td class=example><pre>(nthcdr 2 '(a b c d e))
=> (c d e)
(butnthcdr 2 '(a b c d e))
=> (a b)
</pre></td></tr></table><P>
<A NAME="Destructive list operations"></A>
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<H4> 7.2.1.4 Destructive list operations </H4>
<!--docid::SEC212::-->
<P>
These procedures may mutate the list they operate on, but any such
mutation is undefined.
</P>
<P>
<A NAME="IDX1316"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>nconc</B> <I>args</I>
<DD><CODE>nconc</CODE> destructively concatenates its arguments. (Compare this
with <CODE>append</CODE>, which copies arguments rather than destroying them.)
Sometimes called <CODE>append!</CODE> (see section <A HREF="slib_7.html#SEC239">7.4.4 Rev2 Procedures</A>).
<P>
Example: You want to find the subsets of a set. Here's the obvious way:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(define (subsets set)
(if (null? set)
'(())
(append (map (lambda (sub) (cons (car set) sub))
(subsets (cdr set)))
(subsets (cdr set)))))
</pre></td></tr></table>But that does way more consing than you need. Instead, you could
replace the <CODE>append</CODE> with <CODE>nconc</CODE>, since you don't have any
need for all the intermediate results.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(define x '(a b c))
(define y '(d e f))
(nconc x y)
=> (a b c d e f)
x
=> (a b c d e f)
</pre></td></tr></table><P>
<CODE>nconc</CODE> is the same as <CODE>append!</CODE> in `<TT>sc2.scm</TT>'.
</P>
</DL>
<P>
<A NAME="IDX1317"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>nreverse</B> <I>lst</I>
<DD><CODE>nreverse</CODE> reverses the order of elements in <VAR>lst</VAR> by mutating
<CODE>cdr</CODE>s of the list. Sometimes called <CODE>reverse!</CODE>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(define foo '(a b c))
(nreverse foo)
=> (c b a)
foo
=> (a)
</pre></td></tr></table><P>
Some people have been confused about how to use <CODE>nreverse</CODE>,
thinking that it doesn't return a value. It needs to be pointed out
that
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(set! lst (nreverse lst))
</pre></td></tr></table>is the proper usage, not
<TABLE><tr><td> </td><td class=example><pre>(nreverse lst)
</pre></td></tr></table>The example should suffice to show why this is the case.
</DL>
<P>
<A NAME="IDX1318"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>delete</B> <I>elt lst</I>
<DD><A NAME="IDX1319"></A>
<DT><U>Procedure:</U> <B>delete-if</B> <I>pred lst</I>
<DD><A NAME="IDX1320"></A>
<DT><U>Procedure:</U> <B>delete-if-not</B> <I>pred lst</I>
<DD>Destructive versions of <CODE>remove</CODE> <CODE>remove-if</CODE>, and
<CODE>remove-if-not</CODE>.
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(define lst (list 'foo 'bar 'baz 'bang))
(delete 'foo lst)
=> (bar baz bang)
lst
=> (foo bar baz bang)
(define lst (list 1 2 3 4 5 6 7 8 9))
(delete-if odd? lst)
=> (2 4 6 8)
lst
=> (1 2 4 6 8)
</pre></td></tr></table><P>
Some people have been confused about how to use <CODE>delete</CODE>,
<CODE>delete-if</CODE>, and <CODE>delete-if</CODE>, thinking that they don't return
a value. It needs to be pointed out that
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(set! lst (delete el lst))
</pre></td></tr></table>is the proper usage, not
<TABLE><tr><td> </td><td class=example><pre>(delete el lst)
</pre></td></tr></table>The examples should suffice to show why this is the case.
</DL>
<P>
<A NAME="Non-List functions"></A>
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</TR></TABLE>
<H4> 7.2.1.5 Non-List functions </H4>
<!--docid::SEC213::-->
<P>
<A NAME="IDX1321"></A>
</P>
<DL>
<DT><U>Function:</U> <B>and?</B> <I>arg1 <small>...</small></I>
<DD><CODE>and?</CODE> checks to see if all its arguments are true. If they are,
<CODE>and?</CODE> returns <CODE>#t</CODE>, otherwise, <CODE>#f</CODE>. (In contrast to
<CODE>and</CODE>, this is a function, so all arguments are always evaluated
and in an unspecified order.)
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(and? 1 2 3)
=> #t
(and #f 1 2)
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1322"></A>
</P>
<DL>
<DT><U>Function:</U> <B>or?</B> <I>arg1 <small>...</small></I>
<DD><CODE>or?</CODE> checks to see if any of its arguments are true. If any is
true, <CODE>or?</CODE> returns <CODE>#t</CODE>, and <CODE>#f</CODE> otherwise. (To
<CODE>or</CODE> as <CODE>and?</CODE> is to <CODE>and</CODE>.)
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(or? 1 2 #f)
=> #t
(or? #f #f #f)
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1323"></A>
</P>
<DL>
<DT><U>Function:</U> <B>atom?</B> <I>object</I>
<DD>Returns <CODE>#t</CODE> if <VAR>object</VAR> is not a pair and <CODE>#f</CODE> if it is
pair. (Called <CODE>atom</CODE> in Common LISP.)
<TABLE><tr><td> </td><td class=example><pre>(atom? 1)
=> #t
(atom? '(1 2))
=> #f
(atom? #(1 2)) ; dubious!
=> #t
</pre></td></tr></table></DL>
<P>
<A NAME="Tree Operations"></A>
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<H3> 7.2.2 Tree operations </H3>
<!--docid::SEC214::-->
<P>
<CODE>(require 'tree)</CODE>
<A NAME="IDX1324"></A>
</P>
<P>
These are operations that treat lists a representations of trees.
</P>
<P>
<A NAME="IDX1325"></A>
</P>
<DL>
<DT><U>Function:</U> <B>subst</B> <I>new old tree</I>
<DD><A NAME="IDX1326"></A>
<DT><U>Function:</U> <B>substq</B> <I>new old tree</I>
<DD><A NAME="IDX1327"></A>
<DT><U>Function:</U> <B>substv</B> <I>new old tree</I>
<DD><P>
<A NAME="IDX1328"></A>
<DT><U>Function:</U> <B>subst</B> <I>new old tree equ?</I>
<DD><CODE>subst</CODE> makes a copy of <VAR>tree</VAR>, substituting <VAR>new</VAR> for
every subtree or leaf of <VAR>tree</VAR> which is <CODE>equal?</CODE> to <VAR>old</VAR>
and returns a modified tree. The original <VAR>tree</VAR> is unchanged, but
may share parts with the result.
</P>
<P>
<CODE>substq</CODE> and <CODE>substv</CODE> are similar, but test against <VAR>old</VAR>
using <CODE>eq?</CODE> and <CODE>eqv?</CODE> respectively. If <CODE>subst</CODE> is
called with a fourth argument, <VAR>equ?</VAR> is the equality predicate.
</P>
<P>
Examples:
<TABLE><tr><td> </td><td class=example><pre>(substq 'tempest 'hurricane '(shakespeare wrote (the hurricane)))
=> (shakespeare wrote (the tempest))
(substq 'foo '() '(shakespeare wrote (twelfth night)))
=> (shakespeare wrote (twelfth night . foo) . foo)
(subst '(a . cons) '(old . pair)
'((old . spice) ((old . shoes) old . pair) (old . pair)))
=> ((old . spice) ((old . shoes) a . cons) (a . cons))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1329"></A>
</P>
<DL>
<DT><U>Function:</U> <B>copy-tree</B> <I>tree</I>
<DD><P>
Makes a copy of the nested list structure <VAR>tree</VAR> using new pairs and
returns it. All levels are copied, so that none of the pairs in the
tree are <CODE>eq?</CODE> to the original ones -- only the leaves are.
</P>
<P>
Example:
<TABLE><tr><td> </td><td class=example><pre>(define bar '(bar))
(copy-tree (list bar 'foo))
=> ((bar) foo)
(eq? bar (car (copy-tree (list bar 'foo))))
=> #f
</pre></td></tr></table></DL>
<P>
<A NAME="Chapter Ordering"></A>
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<H3> 7.2.3 Chapter Ordering </H3>
<!--docid::SEC215::-->
<P>
<CODE>(require 'chapter-order)</CODE>
<A NAME="IDX1330"></A>
</P>
<P>
The `<SAMP>chap:</SAMP>' functions deal with strings which are ordered like
chapter numbers (or letters) in a book. Each section of the string
consists of consecutive numeric or consecutive aphabetic characters of
like case.
</P>
<P>
<A NAME="IDX1331"></A>
</P>
<DL>
<DT><U>Function:</U> <B>chap:string<?</B> <I>string1 string2</I>
<DD><P>
Returns #t if the first non-matching run of alphabetic upper-case or
the first non-matching run of alphabetic lower-case or the first
non-matching run of numeric characters of <VAR>string1</VAR> is
<CODE>string<?</CODE> than the corresponding non-matching run of
characters of <VAR>string2</VAR>.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(chap:string<? "a.9" "a.10") => #t
(chap:string<? "4c" "4aa") => #t
(chap:string<? "Revised^{3.99}" "Revised^{4}") => #t
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1332"></A>
</P>
<DL>
<DT><U>Function:</U> <B>chap:string>?</B> <I>string1 string2</I>
<DD><A NAME="IDX1333"></A>
<DT><U>Function:</U> <B>chap:string<=?</B> <I>string1 string2</I>
<DD><A NAME="IDX1334"></A>
<DT><U>Function:</U> <B>chap:string>=?</B> <I>string1 string2</I>
<DD><P>
Implement the corresponding chapter-order predicates.
</P>
</DL>
<P>
<A NAME="IDX1335"></A>
</P>
<DL>
<DT><U>Function:</U> <B>chap:next-string</B> <I>string</I>
<DD><P>
Returns the next string in the <EM>chapter order</EM>. If <VAR>string</VAR>
has no alphabetic or numeric characters,
<CODE>(string-append <VAR>string</VAR> "0")</CODE> is returnd. The argument to
chap:next-string will always be <CODE>chap:string<?</CODE> than the result.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(chap:next-string "a.9") => "a.10"
(chap:next-string "4c") => "4d"
(chap:next-string "4z") => "4aa"
(chap:next-string "Revised^{4}") => "Revised^{5}"
</pre></td></tr></table></DL>
<P>
<A NAME="Sorting"></A>
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<H3> 7.2.4 Sorting </H3>
<!--docid::SEC216::-->
<P>
<CODE>(require 'sort)</CODE>
<A NAME="IDX1336"></A>
</P>
<P>
Many Scheme systems provide some kind of sorting functions. They do
not, however, always provide the <EM>same</EM> sorting functions, and
those that I have had the opportunity to test provided inefficient ones
(a common blunder is to use quicksort which does not perform well).
</P>
<P>
Because <CODE>sort</CODE> and <CODE>sort!</CODE> are not in the standard, there is
very little agreement about what these functions look like. For
example, Dybvig says that Chez Scheme provides
<TABLE><tr><td> </td><td class=example><pre>(merge predicate list1 list2)
(merge! predicate list1 list2)
(sort predicate list)
(sort! predicate list)
</pre></td></tr></table>while MIT Scheme 7.1, following Common LISP, offers unstable
<TABLE><tr><td> </td><td class=example><pre>(sort list predicate)
</pre></td></tr></table>TI PC Scheme offers
<TABLE><tr><td> </td><td class=example><pre>(sort! list/vector predicate?)
</pre></td></tr></table>and Elk offers
<TABLE><tr><td> </td><td class=example><pre>(sort list/vector predicate?)
(sort! list/vector predicate?)
</pre></td></tr></table><P>
Here is a comprehensive catalogue of the variations I have found.
</P>
<P>
<OL>
<LI>
Both <CODE>sort</CODE> and <CODE>sort!</CODE> may be provided.
<LI>
<CODE>sort</CODE> may be provided without <CODE>sort!</CODE>.
<LI>
<CODE>sort!</CODE> may be provided without <CODE>sort</CODE>.
<LI>
Neither may be provided.
<LI>
The sequence argument may be either a list or a vector.
<LI>
The sequence argument may only be a list.
<LI>
The sequence argument may only be a vector.
<LI>
The comparison function may be expected to behave like <CODE><</CODE>.
<LI>
The comparison function may be expected to behave like <CODE><=</CODE>.
<LI>
The interface may be <CODE>(sort predicate? sequence)</CODE>.
<LI>
The interface may be <CODE>(sort sequence predicate?)</CODE>.
<LI>
The interface may be <CODE>(sort sequence &optional (predicate? <))</CODE>.
<LI>
The sort may be stable.
<LI>
The sort may be unstable.
</OL>
<P>
All of this variation really does not help anybody. A nice simple merge
sort is both stable and fast (quite a lot faster than <EM>quick</EM> sort).
</P>
<P>
I am providing this source code with no restrictions at all on its use
(but please retain D.H.D.Warren's credit for the original idea). You
may have to rename some of these functions in order to use them in a
system which already provides incompatible or inferior sorts. For each
of the functions, only the top-level define needs to be edited to do
that.
</P>
<P>
I could have given these functions names which would not clash with any
Scheme that I know of, but I would like to encourage implementors to
converge on a single interface, and this may serve as a hint. The
argument order for all functions has been chosen to be as close to
Common LISP as made sense, in order to avoid NIH-itis.
</P>
<P>
Each of the five functions has a required <EM>last</EM> parameter which is
a comparison function. A comparison function <CODE>f</CODE> is a function of
2 arguments which acts like <CODE><</CODE>. For example,
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(not (f x x))
(and (f x y) (f y z)) == (f x z)
</pre></td></tr></table><P>
The standard functions <CODE><</CODE>, <CODE>></CODE>, <CODE>char<?</CODE>, <CODE>char>?</CODE>,
<CODE>char-ci<?</CODE>, <CODE>char-ci>?</CODE>, <CODE>string<?</CODE>, <CODE>string>?</CODE>,
<CODE>string-ci<?</CODE>, and <CODE>string-ci>?</CODE> are suitable for use as
comparison functions. Think of <CODE>(less? x y)</CODE> as saying when
<CODE>x</CODE> must <EM>not</EM> precede <CODE>y</CODE>.
</P>
<P>
<A NAME="IDX1337"></A>
</P>
<DL>
<DT><U>Function:</U> <B>sorted?</B> <I>sequence less?</I>
<DD>Returns <CODE>#t</CODE> when the sequence argument is in non-decreasing order
according to <VAR>less?</VAR> (that is, there is no adjacent pair <CODE><small>...</small> x
y <small>...</small></CODE> for which <CODE>(less? y x)</CODE>).
<P>
Returns <CODE>#f</CODE> when the sequence contains at least one out-of-order
pair. It is an error if the sequence is not a list, vector, or
string.
</P>
</DL>
<P>
<A NAME="IDX1338"></A>
</P>
<DL>
<DT><U>Function:</U> <B>merge</B> <I>list1 list2 less?</I>
<DD>This merges two lists, producing a completely new list as result. I
gave serious consideration to producing a Common-LISP-compatible
version. However, Common LISP's <CODE>sort</CODE> is our <CODE>sort!</CODE> (well,
in fact Common LISP's <CODE>stable-sort</CODE> is our <CODE>sort!</CODE>, merge sort
is <EM>fast</EM> as well as stable!) so adapting CL code to Scheme takes a
bit of work anyway. I did, however, appeal to CL to determine the
<EM>order</EM> of the arguments.
</DL>
<P>
<A NAME="IDX1339"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>merge!</B> <I>list1 list2 less?</I>
<DD>Merges two lists, re-using the pairs of <VAR>list1</VAR> and <VAR>list2</VAR> to
build the result. If the code is compiled, and <VAR>less?</VAR> constructs
no new pairs, no pairs at all will be allocated. The first pair of the
result will be either the first pair of <VAR>list1</VAR> or the first pair of
<VAR>list2</VAR>, but you can't predict which.
<P>
The code of <CODE>merge</CODE> and <CODE>merge!</CODE> could have been quite a bit
simpler, but they have been coded to reduce the amount of work done per
iteration. (For example, we only have one <CODE>null?</CODE> test per
iteration.)
</P>
<P>
</P>
</DL>
<P>
<A NAME="IDX1340"></A>
</P>
<DL>
<DT><U>Function:</U> <B>sort</B> <I>sequence less?</I>
<DD>Accepts either a list, vector, or string; and returns a new sequence
which is sorted. The new sequence is the same type as the input.
Always <CODE>(sorted? (sort sequence less?) less?)</CODE>. The original
sequence is not altered in any way. The new sequence shares its
<EM>elements</EM> with the old one; no elements are copied.
</DL>
<P>
<A NAME="IDX1341"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>sort!</B> <I>sequence less?</I>
<DD>Returns its sorted result in the original boxes. If the original
sequence is a list, no new storage is allocated at all. If the
original sequence is a vector or string, the sorted elements are put
back in the same vector or string.
<P>
Some people have been confused about how to use <CODE>sort!</CODE>, thinking
that it doesn't return a value. It needs to be pointed out that
<TABLE><tr><td> </td><td class=example><pre>(set! slist (sort! slist <))
</pre></td></tr></table>is the proper usage, not
<TABLE><tr><td> </td><td class=example><pre>(sort! slist <)
</pre></td></tr></table></DL>
<P>
Note that these functions do <EM>not</EM> accept a CL-style `<SAMP>:key</SAMP>'
argument. A simple device for obtaining the same expressiveness is to
define
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(define (keyed less? key)
(lambda (x y) (less? (key x) (key y))))
</pre></td></tr></table>and then, when you would have written
<TABLE><tr><td> </td><td class=example><pre>(sort a-sequence #'my-less :key #'my-key)
</pre></td></tr></table>in Common LISP, just write
<TABLE><tr><td> </td><td class=example><pre>(sort! a-sequence (keyed my-less? my-key))
</pre></td></tr></table>in Scheme.
<P>
<A NAME="Topological Sort"></A>
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<H3> 7.2.5 Topological Sort </H3>
<!--docid::SEC217::-->
<P>
<CODE>(require 'topological-sort)</CODE> or <CODE>(require 'tsort)</CODE>
<A NAME="IDX1342"></A>
<A NAME="IDX1343"></A>
</P>
<P>
The algorithm is inspired by Cormen, Leiserson and Rivest (1990)
<CITE>Introduction to Algorithms</CITE>, chapter 23.
</P>
<P>
<A NAME="IDX1344"></A>
</P>
<DL>
<DT><U>Function:</U> <B>tsort</B> <I>dag pred</I>
<DD><P>
<A NAME="IDX1345"></A>
<DT><U>Function:</U> <B>topological-sort</B> <I>dag pred</I>
<DD>where
</P>
<DL COMPACT>
<DT><VAR>dag</VAR>
<DD>is a list of sublists. The car of each sublist is a vertex. The cdr is
the adjacency list of that vertex, i.e. a list of all vertices to which
there exists an edge from the car vertex.
<DT><VAR>pred</VAR>
<DD>is one of <CODE>eq?</CODE>, <CODE>eqv?</CODE>, <CODE>equal?</CODE>, <CODE>=</CODE>,
<CODE>char=?</CODE>, <CODE>char-ci=?</CODE>, <CODE>string=?</CODE>, or <CODE>string-ci=?</CODE>.
</DL>
<P>
Sort the directed acyclic graph <VAR>dag</VAR> so that for every edge from
vertex <VAR>u</VAR> to <VAR>v</VAR>, <VAR>u</VAR> will come before <VAR>v</VAR> in the
resulting list of vertices.
</P>
<P>
Time complexity: O (|V| + |E|)
</P>
<P>
Example (from Cormen):
<BLOCKQUOTE>
Prof. Bumstead topologically sorts his clothing when getting
dressed. The first argument to <CODE>tsort</CODE> describes which
garments he needs to put on before others. (For example,
Prof Bumstead needs to put on his shirt before he puts on his
tie or his belt.) <CODE>tsort</CODE> gives the correct order of dressing:
</BLOCKQUOTE>
<P>
<TABLE><tr><td> </td><td class=example><pre>(require 'tsort)
<A NAME="IDX1346"></A>(tsort '((shirt tie belt)
(tie jacket)
(belt jacket)
(watch)
(pants shoes belt)
(undershorts pants shoes)
(socks shoes))
eq?)
=>
(socks undershorts pants shoes watch shirt belt tie jacket)
</pre></td></tr></table></DL>
<P>
<A NAME="Hashing"></A>
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<H3> 7.2.6 Hashing </H3>
<!--docid::SEC218::-->
<P>
<CODE>(require 'hash)</CODE>
<A NAME="IDX1347"></A>
</P>
<P>
These hashing functions are for use in quickly classifying objects.
Hash tables use these functions.
</P>
<P>
<A NAME="IDX1348"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hashq</B> <I>obj k</I>
<DD><A NAME="IDX1349"></A>
<DT><U>Function:</U> <B>hashv</B> <I>obj k</I>
<DD><A NAME="IDX1350"></A>
<DT><U>Function:</U> <B>hash</B> <I>obj k</I>
<DD>Returns an exact non-negative integer less than <VAR>k</VAR>. For each
non-negative integer less than <VAR>k</VAR> there are arguments <VAR>obj</VAR> for
which the hashing functions applied to <VAR>obj</VAR> and <VAR>k</VAR> returns
that integer.
<P>
For <CODE>hashq</CODE>, <CODE>(eq? obj1 obj2)</CODE> implies <CODE>(= (hashq obj1 k)
(hashq obj2))</CODE>.
</P>
<P>
For <CODE>hashv</CODE>, <CODE>(eqv? obj1 obj2)</CODE> implies <CODE>(= (hashv obj1 k)
(hashv obj2))</CODE>.
</P>
<P>
For <CODE>hash</CODE>, <CODE>(equal? obj1 obj2)</CODE> implies <CODE>(= (hash obj1 k)
(hash obj2))</CODE>.
</P>
<P>
<CODE>hash</CODE>, <CODE>hashv</CODE>, and <CODE>hashq</CODE> return in time bounded by a
constant. Notice that items having the same <CODE>hash</CODE> implies the
items have the same <CODE>hashv</CODE> implies the items have the same
<CODE>hashq</CODE>.
</P>
</DL>
<P>
<A NAME="Space-Filling Curves"></A>
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<H3> 7.2.7 Space-Filling Curves </H3>
<!--docid::SEC219::-->
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC220">7.2.7.1 Peano-Hilbert Space-Filling Curve</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC221">7.2.7.2 Sierpinski Curve</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
</TABLE>
<P>
<A NAME="Peano-Hilbert Space-Filling Curve"></A>
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<H4> 7.2.7.1 Peano-Hilbert Space-Filling Curve </H4>
<!--docid::SEC220::-->
<P>
<CODE>(require 'hilbert-fill)</CODE>
<A NAME="IDX1351"></A>
</P>
<P>
<A NAME="IDX1352"></A>
<A NAME="IDX1353"></A>
<A NAME="IDX1354"></A>
The <EM>Peano-Hilbert Space-Filling Curve</EM> is a one-to-one mapping
<A NAME="IDX1355"></A>
between a unit line segment and an <VAR>n</VAR>-dimensional unit cube.
</P>
<P>
The integer procedures map the non-negative integers to an
arbitrarily large <VAR>n</VAR>-dimensional cube with its corner at the
origin and all coordinates are non-negative.
</P>
<P>
For any exact nonnegative integers <VAR>scalar</VAR> and <VAR>rank</VAR>,
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(= <VAR>scalar</VAR> (hilbert-coordinates->integer
(integer->hilbert-coordinates <VAR>scalar</VAR> <VAR>rank</VAR>)))
=> #t
</pre></td></tr></table><P>
<A NAME="IDX1356"></A>
</P>
<DL>
<DT><U>Function:</U> <B>integer->hilbert-coordinates</B> <I>scalar rank</I>
<DD><P>
Returns a list of <VAR>rank</VAR> integer coordinates corresponding to exact
non-negative integer <VAR>scalar</VAR>. The lists returned by <CODE>integer->hilbert-coordinates</CODE> for <VAR>scalar</VAR> arguments
0 and 1 will differ in the first element.
</P>
</DL>
<P>
<A NAME="IDX1357"></A>
</P>
<DL>
<DT><U>Function:</U> <B>hilbert-coordinates->integer</B> <I>coords</I>
<DD><P>
Returns an exact non-negative integer corresponding to <VAR>coords</VAR>, a list
of non-negative integer coordinates.
</P>
</DL>
<P>
<A NAME="Sierpinski Curve"></A>
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<H4> 7.2.7.2 Sierpinski Curve </H4>
<!--docid::SEC221::-->
<P>
<CODE>(require 'sierpinski)</CODE>
<A NAME="IDX1358"></A>
</P>
<P>
<A NAME="IDX1359"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-sierpinski-indexer</B> <I>max-coordinate</I>
<DD>Returns a procedure (eg hash-function) of 2 numeric arguments which
preserves <EM>nearness</EM> in its mapping from NxN to N.
<P>
<VAR>max-coordinate</VAR> is the maximum coordinate (a positive integer) of a
population of points. The returned procedures is a function that takes
the x and y coordinates of a point, (non-negative integers) and returns
an integer corresponding to the relative position of that point along a
Sierpinski curve. (You can think of this as computing a (pseudo-)
inverse of the Sierpinski spacefilling curve.)
</P>
<P>
Example use: Make an indexer (hash-function) for integer points lying in
square of integer grid points [0,99]x[0,99]:
<TABLE><tr><td> </td><td class=example><pre>(define space-key (make-sierpinski-indexer 100))
</pre></td></tr></table>Now let's compute the index of some points:
<TABLE><tr><td> </td><td class=example><pre>(space-key 24 78) => 9206
(space-key 23 80) => 9172
</pre></td></tr></table><P>
Note that locations (24, 78) and (23, 80) are near in index and
therefore, because the Sierpinski spacefilling curve is continuous, we
know they must also be near in the plane. Nearness in the plane does
not, however, necessarily correspond to nearness in index, although it
<EM>tends</EM> to be so.
</P>
<P>
Example applications:
<UL>
<LI>
Sort points by Sierpinski index to get heuristic solution to
<EM>travelling salesman problem</EM>. For details of performance,
see L. Platzman and J. Bartholdi, "Spacefilling curves and the
Euclidean travelling salesman problem", JACM 36(4):719--737
(October 1989) and references therein.
<P>
</P>
<LI>
Use Sierpinski index as key by which to store 2-dimensional data
in a 1-dimensional data structure (such as a table). Then
locations that are near each other in 2-d space will tend to
be near each other in 1-d data structure; and locations that
are near in 1-d data structure will be near in 2-d space. This
can significantly speed retrieval from secondary storage because
contiguous regions in the plane will tend to correspond to
contiguous regions in secondary storage. (This is a standard
technique for managing CAD/CAM or geographic data.)
<P>
</UL>
</DL>
<P>
<A NAME="Soundex"></A>
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<H3> 7.2.8 Soundex </H3>
<!--docid::SEC222::-->
<P>
<CODE>(require 'soundex)</CODE>
<A NAME="IDX1360"></A>
</P>
<P>
<A NAME="IDX1361"></A>
</P>
<DL>
<DT><U>Function:</U> <B>soundex</B> <I>name</I>
<DD>Computes the <EM>soundex</EM> hash of <VAR>name</VAR>. Returns a string of an
initial letter and up to three digits between 0 and 6. Soundex
supposedly has the property that names that sound similar in normal
English pronunciation tend to map to the same key.
<P>
Soundex was a classic algorithm used for manual filing of personal
records before the advent of computers. It performs adequately for
English names but has trouble with other languages.
</P>
<P>
See Knuth, Vol. 3 <CITE>Sorting and searching</CITE>, pp 391--2
</P>
<P>
To manage unusual inputs, <CODE>soundex</CODE> omits all non-alphabetic
characters. Consequently, in this implementation:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(soundex <string of blanks>) => ""
(soundex "") => ""
</pre></td></tr></table><P>
Examples from Knuth:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(map soundex '("Euler" "Gauss" "Hilbert" "Knuth"
"Lloyd" "Lukasiewicz"))
=> ("E460" "G200" "H416" "K530" "L300" "L222")
(map soundex '("Ellery" "Ghosh" "Heilbronn" "Kant"
"Ladd" "Lissajous"))
=> ("E460" "G200" "H416" "K530" "L300" "L222")
</pre></td></tr></table><P>
Some cases in which the algorithm fails (Knuth):
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(map soundex '("Rogers" "Rodgers")) => ("R262" "R326")
(map soundex '("Sinclair" "St. Clair")) => ("S524" "S324")
(map soundex '("Tchebysheff" "Chebyshev")) => ("T212" "C121")
</pre></td></tr></table></DL>
<P>
<A NAME="String Search"></A>
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</TR></TABLE>
<H3> 7.2.9 String Search </H3>
<!--docid::SEC223::-->
<P>
<CODE>(require 'string-search)</CODE>
<A NAME="IDX1362"></A>
</P>
<P>
<A NAME="IDX1363"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>string-index</B> <I>string char</I>
<DD><A NAME="IDX1364"></A>
<DT><U>Procedure:</U> <B>string-index-ci</B> <I>string char</I>
<DD>Returns the index of the first occurence of <VAR>char</VAR> within
<VAR>string</VAR>, or <CODE>#f</CODE> if the <VAR>string</VAR> does not contain a
character <VAR>char</VAR>.
</DL>
<P>
<A NAME="IDX1365"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>string-reverse-index</B> <I>string char</I>
<DD><A NAME="IDX1366"></A>
<DT><U>Procedure:</U> <B>string-reverse-index-ci</B> <I>string char</I>
<DD>Returns the index of the last occurence of <VAR>char</VAR> within
<VAR>string</VAR>, or <CODE>#f</CODE> if the <VAR>string</VAR> does not contain a
character <VAR>char</VAR>.
</DL>
<P>
<A NAME="IDX1367"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>substring?</B> <I>pattern string</I>
<DD><A NAME="IDX1368"></A>
<DT><U>Procedure:</U> <B>substring-ci?</B> <I>pattern string</I>
<DD>Searches <VAR>string</VAR> to see if some substring of <VAR>string</VAR> is equal
to <VAR>pattern</VAR>. <CODE>substring?</CODE> returns the index of the first
character of the first substring of <VAR>string</VAR> that is equal to
<VAR>pattern</VAR>; or <CODE>#f</CODE> if <VAR>string</VAR> does not contain
<VAR>pattern</VAR>.
<P>
<TABLE><tr><td> </td><td class=example><pre>(substring? "rat" "pirate") => 2
(substring? "rat" "outrage") => #f
(substring? "" any-string) => 0
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1369"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>find-string-from-port?</B> <I>str in-port max-no-chars</I>
<DD>Looks for a string <VAR>str</VAR> within the first <VAR>max-no-chars</VAR> chars
of the input port <VAR>in-port</VAR>.
<P>
<A NAME="IDX1370"></A>
<DT><U>Procedure:</U> <B>find-string-from-port?</B> <I>str in-port</I>
<DD>When called with two arguments, the search span is limited by the end of
the input stream.
</P>
<P>
<A NAME="IDX1371"></A>
<DT><U>Procedure:</U> <B>find-string-from-port?</B> <I>str in-port char</I>
<DD>Searches up to the first occurrence of character <VAR>char</VAR> in
<VAR>str</VAR>.
</P>
<P>
<A NAME="IDX1372"></A>
<DT><U>Procedure:</U> <B>find-string-from-port?</B> <I>str in-port proc</I>
<DD>Searches up to the first occurrence of the procedure <VAR>proc</VAR>
returning non-false when called with a character (from <VAR>in-port</VAR>)
argument.
</P>
<P>
When the <VAR>str</VAR> is found, <CODE>find-string-from-port?</CODE> returns the
number of characters it has read from the port, and the port is set to
read the first char after that (that is, after the <VAR>str</VAR>) The
function returns <CODE>#f</CODE> when the <VAR>str</VAR> isn't found.
</P>
<P>
<CODE>find-string-from-port?</CODE> reads the port <EM>strictly</EM>
sequentially, and does not perform any buffering. So
<CODE>find-string-from-port?</CODE> can be used even if the <VAR>in-port</VAR> is
open to a pipe or other communication channel.
</P>
</DL>
<P>
<A NAME="IDX1373"></A>
</P>
<DL>
<DT><U>Function:</U> <B>string-subst</B> <I>txt old1 new1 <small>...</small></I>
<DD>Returns a copy of string <VAR>txt</VAR> with all occurrences of string
<VAR>old1</VAR> in <VAR>txt</VAR> replaced with <VAR>new1</VAR>; then <VAR>old2</VAR>
replaced with <VAR>new2</VAR> <small>...</small>. Matches are found from the left.
Matches do not overlap.
</DL>
<P>
<A NAME="IDX1374"></A>
</P>
<DL>
<DT><U>Function:</U> <B>count-newlines</B> <I>str</I>
<DD>Returns the number of `<SAMP>#\newline</SAMP>' characters in string <VAR>str</VAR>.
</DL>
<P>
<A NAME="Sequence Comparison"></A>
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</TR></TABLE>
<H3> 7.2.10 Sequence Comparison </H3>
<!--docid::SEC224::-->
<P>
<CODE>(require 'diff)</CODE>
<A NAME="IDX1375"></A>
<A NAME="IDX1376"></A>
</P>
<P>
<CODE>diff:edit-length</CODE> implements the algorithm:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>S. Wu, E. Myers, U. Manber, and W. Miller,
"An O(NP) Sequence Comparison Algorithm,"
Information Processing Letters 35, 6 (1990), 317-323.
<A HREF="http://www.cs.arizona.edu/people/gene/vita.html">http://www.cs.arizona.edu/people/gene/vita.html</A>
</pre></td></tr></table>S. Wu, <A HREF="http://www.cs.arizona.edu/people/gene/vita.html">
E. Myers,</A> U. Manber, and W. Miller,
<A HREF="http://www.cs.arizona.edu/people/gene/PAPERS/np_diff.ps">
"An O(NP) Sequence Comparison Algorithm,"</A>
Information Processing Letters 35, 6 (1990), 317-323.
<P>
The values returned by <CODE>diff:edit-length</CODE> can be used to gauge
the degree of match between two sequences.
</P>
<P>
Surprisingly, "An O(NP) Sequence Comparison Algorithm" does not
derive the edit sequence; only the sequence length. Developing this
linear-space sub-quadratic-time algorithm for computing the edit
sequence required hundreds of hours of work. I have submitted a
paper describing the algorithm to the Journal of Computational
Biology.
</P>
<P>
If the items being sequenced are text lines, then the computed
edit-list is equivalent to the output of the <EM>diff</EM> utility
<A NAME="IDX1377"></A>
program. If the items being sequenced are words, then it is like the
lesser known <EM>spiff</EM> program.
<A NAME="IDX1378"></A>
</P>
<P>
<A NAME="IDX1379"></A>
</P>
<DL>
<DT><U>Function:</U> <B>diff:longest-common-subsequence</B> <I>array1 array2 =? p-lim</I>
<DD><P>
<A NAME="IDX1380"></A>
<DT><U>Function:</U> <B>diff:longest-common-subsequence</B> <I>array1 array2 =?</I>
<DD><VAR>array1</VAR> and <VAR>array2</VAR> are one-dimensional arrays. The procedure <VAR>=?</VAR> is used
to compare sequence tokens for equality.
</P>
<P>
The non-negative integer <VAR>p-lim</VAR>, if provided, is maximum number of
deletions of the shorter sequence to allow. <CODE>diff:longest-common-subsequence</CODE> will return <CODE>#f</CODE>
if more deletions would be necessary.
</P>
<P>
<CODE>diff:longest-common-subsequence</CODE> returns a one-dimensional array of length <CODE>(quotient (- (+
len1 len2) (diff:edit-length <VAR>array1</VAR> <VAR>array2</VAR>)) 2)</CODE> holding the longest sequence
common to both <VAR>array</VAR>s.
</P>
</DL>
<P>
<A NAME="IDX1381"></A>
</P>
<DL>
<DT><U>Function:</U> <B>diff:edits</B> <I>array1 array2 =? p-lim</I>
<DD><P>
<A NAME="IDX1382"></A>
<DT><U>Function:</U> <B>diff:edits</B> <I>array1 array2 =?</I>
<DD><VAR>array1</VAR> and <VAR>array2</VAR> are one-dimensional arrays. The procedure <VAR>=?</VAR> is used
to compare sequence tokens for equality.
</P>
<P>
The non-negative integer <VAR>p-lim</VAR>, if provided, is maximum number of
deletions of the shorter sequence to allow. <CODE>diff:edits</CODE> will return <CODE>#f</CODE>
if more deletions would be necessary.
</P>
<P>
<CODE>diff:edits</CODE> returns a vector of length <CODE>(diff:edit-length <VAR>array1</VAR> <VAR>array2</VAR>)</CODE> composed
of a shortest sequence of edits transformaing <VAR>array1</VAR> to <VAR>array2</VAR>.
</P>
<P>
Each edit is an integer:
</P>
<DL COMPACT>
<DT><VAR>k</VAR> > 0
<DD>Inserts <CODE>(array-ref <VAR>array1</VAR> (+ -1 <VAR>j</VAR>))</CODE> into the sequence.
<DT><VAR>k</VAR> < 0
<DD>Deletes <CODE>(array-ref <VAR>array2</VAR> (- -1 <VAR>k</VAR>))</CODE> from the sequence.
</DL>
</DL>
<P>
<A NAME="IDX1383"></A>
</P>
<DL>
<DT><U>Function:</U> <B>diff:edit-length</B> <I>array1 array2 =? p-lim</I>
<DD><P>
<A NAME="IDX1384"></A>
<DT><U>Function:</U> <B>diff:edit-length</B> <I>array1 array2 =?</I>
<DD><VAR>array1</VAR> and <VAR>array2</VAR> are one-dimensional arrays. The procedure <VAR>=?</VAR> is used
to compare sequence tokens for equality.
</P>
<P>
The non-negative integer <VAR>p-lim</VAR>, if provided, is maximum number of
deletions of the shorter sequence to allow. <CODE>diff:edit-length</CODE> will return <CODE>#f</CODE>
if more deletions would be necessary.
</P>
<P>
<CODE>diff:edit-length</CODE> returns the length of the shortest sequence of edits transformaing
<VAR>array1</VAR> to <VAR>array2</VAR>.
</P>
</DL>
<TABLE><tr><td> </td><td class=example><pre>(diff:longest-common-subsequence "fghiejcklm" "fgehijkpqrlm" eqv?)
=> "fghijklm"
(diff:edit-length "fghiejcklm" "fgehijkpqrlm" eqv?)
=> 6
(diff:edits "fghiejcklm" "fgehijkpqrlm" eqv?)
=> #As32(3 -5 -7 8 9 10)
; e c h p q r
</pre></td></tr></table><P>
<A NAME="Procedures"></A>
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<H2> 7.3 Procedures </H2>
<!--docid::SEC225::-->
<P>
Anything that doesn't fall neatly into any of the other categories winds
up here.
</P>
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC226">7.3.1 Type Coercion</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'coerce</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC227">7.3.2 String-Case</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'string-case</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC228">7.3.3 String Ports</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'string-port</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC229">7.3.4 Line I/O</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'line-i/o</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC230">7.3.5 Multi-Processing</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'process</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC231">7.3.6 Metric Units</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Portable manifest types for numeric values.</TD></TR>
</TABLE>
<P>
<A NAME="Type Coercion"></A>
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</TR></TABLE>
<H3> 7.3.1 Type Coercion </H3>
<!--docid::SEC226::-->
<CODE>(require 'coerce)</CODE>
<A NAME="IDX1385"></A>
<P>
<A NAME="IDX1386"></A>
</P>
<DL>
<DT><U>Function:</U> <B>type-of</B> <I>obj</I>
<DD><P>
Returns a symbol name for the type of <VAR>obj</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1387"></A>
</P>
<DL>
<DT><U>Function:</U> <B>coerce</B> <I>obj result-type</I>
<DD><P>
Converts and returns <VAR>obj</VAR> of type <CODE>char</CODE>, <CODE>number</CODE>,
<CODE>string</CODE>, <CODE>symbol</CODE>, <CODE>list</CODE>, or <CODE>vector</CODE> to
<VAR>result-type</VAR> (which must be one of these symbols).
</P>
</DL>
<P>
<A NAME="String-Case"></A>
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</TR></TABLE>
<H3> 7.3.2 String-Case </H3>
<!--docid::SEC227::-->
<P>
<CODE>(require 'string-case)</CODE>
<A NAME="IDX1388"></A>
</P>
<P>
<A NAME="IDX1389"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>string-upcase</B> <I>str</I>
<DD><A NAME="IDX1390"></A>
<DT><U>Procedure:</U> <B>string-downcase</B> <I>str</I>
<DD><A NAME="IDX1391"></A>
<DT><U>Procedure:</U> <B>string-capitalize</B> <I>str</I>
<DD>The obvious string conversion routines. These are non-destructive.
</DL>
<P>
<A NAME="IDX1392"></A>
</P>
<DL>
<DT><U>Function:</U> <B>string-upcase!</B> <I>str</I>
<DD><A NAME="IDX1393"></A>
<DT><U>Function:</U> <B>string-downcase!</B> <I>str</I>
<DD><A NAME="IDX1394"></A>
<DT><U>Function:</U> <B>string-capitalize!</B> <I>str</I>
<DD>The destructive versions of the functions above.
</DL>
<P>
<A NAME="IDX1395"></A>
</P>
<DL>
<DT><U>Function:</U> <B>string-ci->symbol</B> <I>str</I>
<DD>Converts string <VAR>str</VAR> to a symbol having the same case as if the
symbol had been <CODE>read</CODE>.
</DL>
<P>
<A NAME="IDX1396"></A>
</P>
<DL>
<DT><U>Function:</U> <B>symbol-append</B> <I>obj1 <small>...</small></I>
<DD>Converts <VAR>obj1</VAR> <small>...</small> to strings, appends them, and converts to a
symbol which is returned. Strings and numbers are converted to read's
symbol case; the case of symbol characters is not changed. #f is
converted to the empty string (symbol).
</DL>
<P>
<A NAME="IDX1397"></A>
</P>
<DL>
<DT><U>Function:</U> <B>StudlyCapsExpand</B> <I>str delimiter</I>
<DD><A NAME="IDX1398"></A>
<DT><U>Function:</U> <B>StudlyCapsExpand</B> <I>str</I>
<DD><VAR>delimiter</VAR> must be a string or character. If absent,
<VAR>delimiter</VAR> defaults to `<SAMP>-</SAMP>'. <CODE>StudlyCapsExpand</CODE> returns a
copy of <VAR>str</VAR> where <VAR>delimiter</VAR> is inserted between each
lower-case character immediately followed by an upper-case character;
and between two upper-case characters immediately followed by a
lower-case character.
<P>
<TABLE><tr><td> </td><td class=example><pre>(StudlyCapsExpand "aX" " ") => "a X"
(StudlyCapsExpand "aX" "..") => "a..X"
(StudlyCapsExpand "AX") => "AX"
(StudlyCapsExpand "Ax") => "Ax"
(StudlyCapsExpand "AXLE") => "AXLE"
(StudlyCapsExpand "aAXACz") => "a-AXA-Cz"
(StudlyCapsExpand "AaXACz") => "Aa-XA-Cz"
(StudlyCapsExpand "AAaXACz") => "A-Aa-XA-Cz"
(StudlyCapsExpand "AAaXAC") => "A-Aa-XAC"
</pre></td></tr></table><P>
</P>
</DL>
<P>
<A NAME="String Ports"></A>
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<H3> 7.3.3 String Ports </H3>
<!--docid::SEC228::-->
<P>
<CODE>(require 'string-port)</CODE>
<A NAME="IDX1399"></A>
</P>
<P>
<A NAME="IDX1400"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>call-with-output-string</B> <I>proc</I>
<DD><VAR>proc</VAR> must be a procedure of one argument. This procedure calls
<VAR>proc</VAR> with one argument: a (newly created) output port. When the
function returns, the string composed of the characters written into the
port is returned.
</DL>
<P>
<A NAME="IDX1401"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>call-with-input-string</B> <I>string proc</I>
<DD><VAR>proc</VAR> must be a procedure of one argument. This procedure calls
<VAR>proc</VAR> with one argument: an (newly created) input port from which
<VAR>string</VAR>'s contents may be read. When <VAR>proc</VAR> returns, the port
is closed and the value yielded by the procedure <VAR>proc</VAR> is
returned.
</DL>
<P>
<A NAME="Line I/O"></A>
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<H3> 7.3.4 Line I/O </H3>
<!--docid::SEC229::-->
<P>
<CODE>(require 'line-i/o)</CODE>
<A NAME="IDX1402"></A>
</P>
<P>
<A NAME="IDX1403"></A>
</P>
<DL>
<DT><U>Function:</U> <B>read-line</B>
<DD><P>
<A NAME="IDX1404"></A>
<DT><U>Function:</U> <B>read-line</B> <I>port</I>
<DD>Returns a string of the characters up to, but not including a
newline or end of file, updating <VAR>port</VAR> to point to the
character following the newline. If no characters are available, an
end of file object is returned. The <VAR>port</VAR> argument may be
omitted, in which case it defaults to the value returned by
<CODE>current-input-port</CODE>.
</P>
</DL>
<P>
<A NAME="IDX1405"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>read-line!</B> <I>string</I>
<DD><P>
<A NAME="IDX1406"></A>
<DT><U>Procedure:</U> <B>read-line!</B> <I>string port</I>
<DD>Fills <VAR>string</VAR> with characters up to, but not including a newline or end
of file, updating the <VAR>port</VAR> to point to the last character read
or following the newline if it was read. If no characters are
available, an end of file object is returned. If a newline or end
of file was found, the number of characters read is returned.
Otherwise, <CODE>#f</CODE> is returned. The <VAR>port</VAR> argument may be
omitted, in which case it defaults to the value returned by
<CODE>current-input-port</CODE>.
</P>
</DL>
<P>
<A NAME="IDX1407"></A>
</P>
<DL>
<DT><U>Function:</U> <B>write-line</B> <I>string</I>
<DD><P>
<A NAME="IDX1408"></A>
<DT><U>Function:</U> <B>write-line</B> <I>string port</I>
<DD>Writes <VAR>string</VAR> followed by a newline to the given <VAR>port</VAR> and returns
an unspecified value. The <VAR>Port</VAR> argument may be omitted, in
which case it defaults to the value returned by
<CODE>current-input-port</CODE>.
</P>
</DL>
<P>
<A NAME="IDX1409"></A>
</P>
<DL>
<DT><U>Function:</U> <B>system->line</B> <I>command tmp</I>
<DD><P>
<A NAME="IDX1410"></A>
<DT><U>Function:</U> <B>system->line</B> <I>command</I>
<DD><VAR>command</VAR> must be a string. The string <VAR>tmp</VAR>, if supplied, is a path to use as
a temporary file. <CODE>system->line</CODE> calls <CODE>system</CODE> with <VAR>command</VAR> as argument,
redirecting stdout to file <VAR>tmp</VAR>. <CODE>system->line</CODE> returns a string containing the
first line of output from <VAR>tmp</VAR>.
</P>
</DL>
<P>
<A NAME="Multi-Processing"></A>
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<H3> 7.3.5 Multi-Processing </H3>
<!--docid::SEC230::-->
<P>
<CODE>(require 'process)</CODE>
<A NAME="IDX1411"></A>
</P>
<P>
This module implements asynchronous (non-polled) time-sliced
multi-processing in the SCM Scheme implementation using procedures
<CODE>alarm</CODE> and <CODE>alarm-interrupt</CODE>.
<A NAME="IDX1412"></A>
<A NAME="IDX1413"></A>
Until this is ported to another implementation, consider it an example
of writing schedulers in Scheme.
</P>
<P>
<A NAME="IDX1414"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>add-process!</B> <I>proc</I>
<DD>Adds proc, which must be a procedure (or continuation) capable of
accepting accepting one argument, to the <CODE>process:queue</CODE>. The
value returned is unspecified. The argument to <VAR>proc</VAR> should be
ignored. If <VAR>proc</VAR> returns, the process is killed.
</DL>
<P>
<A NAME="IDX1415"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>process:schedule!</B>
<DD>Saves the current process on <CODE>process:queue</CODE> and runs the next
process from <CODE>process:queue</CODE>. The value returned is
unspecified.
</DL>
<P>
<A NAME="IDX1416"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>kill-process!</B>
<DD>Kills the current process and runs the next process from
<CODE>process:queue</CODE>. If there are no more processes on
<CODE>process:queue</CODE>, <CODE>(slib:exit)</CODE> is called (see section <A HREF="slib_2.html#SEC17">2.4 System</A>).
</DL>
<P>
<A NAME="Metric Units"></A>
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<H3> 7.3.6 Metric Units </H3>
<!--docid::SEC231::-->
<P>
<CODE>(require 'metric-units)</CODE>
<A NAME="IDX1417"></A>
</P>
<P>
<A HREF="http://swissnet.ai.mit.edu/~jaffer/MIXF.html">http://swissnet.ai.mit.edu/~jaffer/MIXF.html</A>
</P>
<P>
<EM>Metric Interchange Format</EM> is a character string encoding for
numerical values and units which:
</P>
<P>
<UL>
<LI>
is unambiguous in all locales;
<P>
</P>
<LI>
uses only [TOG] "Portable Character Set" characters matching "Basic
Latin" characters in Plane 0 of the Universal Character Set [UCS];
<P>
</P>
<LI>
is transparent to [UTF-7] and [UTF-8] UCS transformation formats;
<P>
</P>
<LI>
is human readable and writable;
<P>
</P>
<LI>
is machine readable and writable;
<P>
</P>
<LI>
incorporates SI prefixes and units;
<P>
</P>
<LI>
incorporates [ISO 6093] numbers; and
<P>
</P>
<LI>
incorporates [IEC 60027-2] binary prefixes.
</UL>
<P>
In the expression for the value of a quantity, the unit symbol is placed
after the numerical value. A dot (PERIOD, `<SAMP>.</SAMP>') is placed between
the numerical value and the unit symbol.
</P>
<P>
Within a compound unit, each of the base and derived symbols can
optionally have an attached SI prefix.
</P>
<P>
Unit symbols formed from other unit symbols by multiplication are
indicated by means of a dot (PERIOD, `<SAMP>.</SAMP>') placed between them.
</P>
<P>
Unit symbols formed from other unit symbols by division are indicated by
means of a SOLIDUS (`<SAMP>/</SAMP>') or negative exponents. The SOLIDUS must
not be repeated in the same compound unit unless contained within a
parenthesized subexpression.
</P>
<P>
The grouping formed by a prefix symbol attached to a unit symbol
constitutes a new inseparable symbol (forming a multiple or submultiple
of the unit concerned) which can be raised to a positive or negative
power and which can be combined with other unit symbols to form compound
unit symbols.
</P>
<P>
The grouping formed by surrounding compound unit symbols with
parentheses (`<SAMP>(</SAMP>' and `<SAMP>)</SAMP>') constitutes a new inseparable symbol
which can be raised to a positive or negative power and which can be
combined with other unit symbols to form compound unit symbols.
</P>
<P>
Compound prefix symbols, that is, prefix symbols formed by the
juxtaposition of two or more prefix symbols, are not permitted.
</P>
<P>
Prefix symbols are not used with the time-related unit symbols min
(minute), h (hour), d (day). No prefix symbol may be used with dB
(decibel). Only submultiple prefix symbols may be used with the unit
symbols L (liter), Np (neper), o (degree), oC (degree Celsius), rad
(radian), and sr (steradian). Submultiple prefix symbols may not be
used with the unit symbols t (metric ton), r (revolution), or Bd (baud).
</P>
<P>
A unit exponent follows the unit, separated by a CIRCUMFLEX (`<SAMP>^</SAMP>').
Exponents may be positive or negative. Fractional exponents must be
parenthesized.
</P>
<P>
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<H4> 7.3.6.1 SI Prefixes </H4>
<!--docid::SEC232::-->
<TABLE><tr><td> </td><td class=example><pre> Factor Name Symbol | Factor Name Symbol
====== ==== ====== | ====== ==== ======
1e24 yotta Y | 1e-1 deci d
1e21 zetta Z | 1e-2 centi c
1e18 exa E | 1e-3 milli m
1e15 peta P | 1e-6 micro u
1e12 tera T | 1e-9 nano n
1e9 giga G | 1e-12 pico p
1e6 mega M | 1e-15 femto f
1e3 kilo k | 1e-18 atto a
1e2 hecto h | 1e-21 zepto z
1e1 deka da | 1e-24 yocto y
</pre></td></tr></table><P>
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<H4> 7.3.6.2 Binary Prefixes </H4>
<!--docid::SEC233::-->
<P>
These binary prefixes are valid only with the units B (byte) and bit.
However, decimal prefixes can also be used with bit; and decimal
multiple (not submultiple) prefixes can also be used with B (byte).
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre> Factor (power-of-2) Name Symbol
====== ============ ==== ======
1.152921504606846976e18 (2^60) exbi Ei
1.125899906842624e15 (2^50) pebi Pi
1.099511627776e12 (2^40) tebi Ti
1.073741824e9 (2^30) gibi Gi
1.048576e6 (2^20) mebi Mi
1.024e3 (2^10) kibi Ki
</pre></td></tr></table><P>
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<H4> 7.3.6.3 Unit Symbols </H4>
<!--docid::SEC234::-->
<P>
<TABLE><tr><td> </td><td class=example><pre> Type of Quantity Name Symbol Equivalent
================ ==== ====== ==========
time second s
time minute min = 60.s
time hour h = 60.min
time day d = 24.h
frequency hertz Hz s^-1
signaling rate baud Bd s^-1
length meter m
volume liter L dm^3
plane angle radian rad
solid angle steradian sr rad^2
plane angle revolution * r = 6.283185307179586.rad
plane angle degree * o = 2.777777777777778e-3.r
information capacity bit bit
information capacity byte, octet B = 8.bit
mass gram g
mass ton t Mg
mass unified atomic mass unit u = 1.66053873e-27.kg
amount of substance mole mol
catalytic activity katal kat mol/s
thermodynamic temperature kelvin K
centigrade temperature degree Celsius oC
luminous intensity candela cd
luminous flux lumen lm cd.sr
illuminance lux lx lm/m^2
force newton N m.kg.s^-2
pressure, stress pascal Pa N/m^2
energy, work, heat joule J N.m
energy electronvolt eV = 1.602176462e-19.J
power, radiant flux watt W J/s
logarithm of power ratio neper Np
logarithm of power ratio decibel * dB = 0.1151293.Np
electric current ampere A
electric charge coulomb C s.A
electric potential, EMF volt V W/A
capacitance farad F C/V
electric resistance ohm Ohm V/A
electric conductance siemens S A/V
magnetic flux weber Wb V.s
magnetic flux density tesla T Wb/m^2
inductance henry H Wb/A
radionuclide activity becquerel Bq s^-1
absorbed dose energy gray Gy m^2.s^-2
dose equivalent sievert Sv m^2.s^-2
</pre></td></tr></table><P>
* The formulas are:
</P>
<P>
<UL>
<LI>
r/rad = 8 * atan(1)
<LI>
o/r = 1 / 360
<LI>
db/Np = ln(10) / 20
</UL>
<P>
<A NAME="IDX1418"></A>
</P>
<DL>
<DT><U>Function:</U> <B>si:conversion-factor</B> <I>to-unit from-unit</I>
<DD>If the strings <VAR>from-unit</VAR> and <VAR>to-unit</VAR> express valid unit
expressions for quantities of the same unit-dimensions, then the value
returned by <CODE>si:conversion-factor</CODE> will be such that multiplying a
numerical value expressed in <VAR>from-unit</VAR>s by the returned conversion
factor yields the numerical value expressed in <VAR>to-unit</VAR>s.
<P>
Otherwise, <CODE>si:conversion-factor</CODE> returns:
</P>
<P>
</P>
<DL COMPACT>
<DT>-3
<DD>if neither <VAR>from-unit</VAR> nor <VAR>to-unit</VAR> is a syntactically valid
unit.
<DT>-2
<DD>if <VAR>from-unit</VAR> is not a syntactically valid unit.
<DT>-1
<DD>if <VAR>to-unit</VAR> is not a syntactically valid unit.
<DT>0
<DD>if linear conversion (by a factor) is not possible.
</DL>
<P>
</P>
</DL>
<P>
<TABLE><tr><td> </td><td class=example><pre>(si:conversion-factor "km/s" "m/s" ) => 0.001
(si:conversion-factor "N" "m/s" ) => 0
(si:conversion-factor "moC" "oC" ) => 1000
(si:conversion-factor "mK" "oC" ) => 0
(si:conversion-factor "rad" "o" ) => 0.0174533
(si:conversion-factor "K" "o" ) => 0
(si:conversion-factor "K" "K" ) => 1
(si:conversion-factor "oK" "oK" ) => -3
(si:conversion-factor "" "s/s" ) => 1
(si:conversion-factor "km/h" "mph" ) => -2
</pre></td></tr></table><P>
<A NAME="Standards Support"></A>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 7.4 Standards Support </H2>
<!--docid::SEC235::-->
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC236">7.4.1 RnRS</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Revised Reports on Scheme</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC237">7.4.2 With-File</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'with-file</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC238">7.4.3 Transcripts</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'transcript</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC239">7.4.4 Rev2 Procedures</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'rev2-procedures</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC240">7.4.5 Rev4 Optional Procedures</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'rev4-optional-procedures</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC241">7.4.6 Multi-argument / and -</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'multiarg/and-</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC242">7.4.7 Multi-argument Apply</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'multiarg-apply</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC243">7.4.8 Rationalize</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'rationalize</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC244">7.4.9 Promises</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'delay</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC245">7.4.10 Dynamic-Wind</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'dynamic-wind</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC246">7.4.11 Eval</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'eval</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC247">7.4.12 Values</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'values</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC248">7.4.13 SRFI</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'http://srfi.schemers.org/srfi-0/srfi-0.html</TD></TR>
</TABLE>
<P>
<A NAME="RnRS"></A>
<HR SIZE="6">
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<H3> 7.4.1 RnRS </H3>
<!--docid::SEC236::-->
<P>
The <CODE>r2rs</CODE>, <CODE>r3rs</CODE>, <CODE>r4rs</CODE>, and <CODE>r5rs</CODE> features
attempt to provide procedures and macros to bring a Scheme
implementation to the desired version of Scheme.
</P>
<P>
<A NAME="IDX1419"></A>
</P>
<DL>
<DT><U>Feature:</U> <B>r2rs</B>
<DD><A NAME="IDX1420"></A>
Requires features implementing procedures and optional procedures
specified by <CITE>Revised^2 Report on the Algorithmic Language Scheme</CITE>;
namely <CODE>rev3-procedures</CODE> and <CODE>rev2-procedures</CODE>.
</DL>
<P>
<A NAME="IDX1421"></A>
</P>
<DL>
<DT><U>Feature:</U> <B>r3rs</B>
<DD><A NAME="IDX1422"></A>
Requires features implementing procedures and optional procedures
specified by <CITE>Revised^3 Report on the Algorithmic Language Scheme</CITE>;
namely <CODE>rev3-procedures</CODE>.
<P>
<EM>Note:</EM> SLIB already mandates the <CODE>r3rs</CODE> procedures which can
be portably implemented in <CODE>r4rs</CODE> implementations.
</P>
</DL>
<P>
<A NAME="IDX1423"></A>
</P>
<DL>
<DT><U>Feature:</U> <B>r4rs</B>
<DD><A NAME="IDX1424"></A>
Requires features implementing procedures and optional procedures
specified by <CITE>Revised^4 Report on the Algorithmic Language Scheme</CITE>;
namely <CODE>rev4-optional-procedures</CODE>.
</DL>
<P>
<A NAME="IDX1425"></A>
</P>
<DL>
<DT><U>Feature:</U> <B>r5rs</B>
<DD><A NAME="IDX1426"></A>
Requires features implementing procedures and optional procedures
specified by <CITE>Revised^5 Report on the Algorithmic Language Scheme</CITE>;
namely <CODE>values</CODE>, <CODE>macro</CODE>, and <CODE>eval</CODE>.
</DL>
<P>
<A NAME="With-File"></A>
<HR SIZE="6">
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<H3> 7.4.2 With-File </H3>
<!--docid::SEC237::-->
<P>
<CODE>(require 'with-file)</CODE>
<A NAME="IDX1427"></A>
</P>
<P>
<A NAME="IDX1428"></A>
</P>
<DL>
<DT><U>Function:</U> <B>with-input-from-file</B> <I>file thunk</I>
<DD><A NAME="IDX1429"></A>
<DT><U>Function:</U> <B>with-output-to-file</B> <I>file thunk</I>
<DD>Description found in R4RS.
</DL>
<P>
<A NAME="Transcripts"></A>
<HR SIZE="6">
<A NAME="SEC238"></A>
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</TR></TABLE>
<H3> 7.4.3 Transcripts </H3>
<!--docid::SEC238::-->
<P>
<CODE>(require 'transcript)</CODE>
<A NAME="IDX1430"></A>
</P>
<P>
<A NAME="IDX1431"></A>
</P>
<DL>
<DT><U>Function:</U> <B>transcript-on</B> <I>filename</I>
<DD><A NAME="IDX1432"></A>
<DT><U>Function:</U> <B>transcript-off</B> <I>filename</I>
<DD>Redefines <CODE>read-char</CODE>, <CODE>read</CODE>, <CODE>write-char</CODE>,
<CODE>write</CODE>, <CODE>display</CODE>, and <CODE>newline</CODE>.
</DL>
<P>
<A NAME="Rev2 Procedures"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.4.4 Rev2 Procedures </H3>
<!--docid::SEC239::-->
<P>
<CODE>(require 'rev2-procedures)</CODE>
<A NAME="IDX1433"></A>
</P>
<P>
The procedures below were specified in the <CITE>Revised^2 Report on
Scheme</CITE>. <STRONG>N.B.</STRONG>: The symbols <CODE>1+</CODE> and <CODE>-1+</CODE> are not
<CITE>R4RS</CITE> syntax. Scheme->C, for instance, chokes on this
module.
</P>
<P>
<A NAME="IDX1434"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>substring-move-left!</B> <I>string1 start1 end1 string2 start2</I>
<DD><A NAME="IDX1435"></A>
<DT><U>Procedure:</U> <B>substring-move-right!</B> <I>string1 start1 end1 string2 start2</I>
<DD><VAR>string1</VAR> and <VAR>string2</VAR> must be a strings, and <VAR>start1</VAR>,
<VAR>start2</VAR> and <VAR>end1</VAR> must be exact integers satisfying
<P>
<TABLE><tr><td> </td><td class=display><pre style="font-family: serif">0 <= <VAR>start1</VAR> <= <VAR>end1</VAR> <= (string-length <VAR>string1</VAR>)
0 <= <VAR>start2</VAR> <= <VAR>end1</VAR> - <VAR>start1</VAR> + <VAR>start2</VAR> <= (string-length <VAR>string2</VAR>)
</pre></td></tr></table><P>
<CODE>substring-move-left!</CODE> and <CODE>substring-move-right!</CODE> store
characters of <VAR>string1</VAR> beginning with index <VAR>start1</VAR>
(inclusive) and ending with index <VAR>end1</VAR> (exclusive) into
<VAR>string2</VAR> beginning with index <VAR>start2</VAR> (inclusive).
</P>
<P>
<CODE>substring-move-left!</CODE> stores characters in time order of
increasing indices. <CODE>substring-move-right!</CODE> stores characters in
time order of increasing indeces.
</P>
</DL>
<P>
<A NAME="IDX1436"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>substring-fill!</B> <I>string start end char</I>
<DD>Fills the elements <VAR>start</VAR>--<VAR>end</VAR> of <VAR>string</VAR> with the
character <VAR>char</VAR>.
</DL>
<P>
<A NAME="IDX1437"></A>
</P>
<DL>
<DT><U>Function:</U> <B>string-null?</B> <I>str</I>
<DD>== <CODE>(= 0 (string-length <VAR>str</VAR>))</CODE>
</DL>
<P>
<A NAME="IDX1438"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>append!</B> <I>pair1 <small>...</small></I>
<DD>Destructively appends its arguments. Equivalent to <CODE>nconc</CODE>.
</DL>
<P>
<A NAME="IDX1439"></A>
</P>
<DL>
<DT><U>Function:</U> <B>1+</B> <I>n</I>
<DD>Adds 1 to <VAR>n</VAR>.
</DL>
<P>
<A NAME="IDX1440"></A>
</P>
<DL>
<DT><U>Function:</U> <B>-1+</B> <I>n</I>
<DD>Subtracts 1 from <VAR>n</VAR>.
</DL>
<P>
<A NAME="IDX1441"></A>
</P>
<DL>
<DT><U>Function:</U> <B><?</B>
<DD><A NAME="IDX1442"></A>
<DT><U>Function:</U> <B><=?</B>
<DD><A NAME="IDX1443"></A>
<DT><U>Function:</U> <B>=?</B>
<DD><A NAME="IDX1444"></A>
<DT><U>Function:</U> <B>>?</B>
<DD><A NAME="IDX1445"></A>
<DT><U>Function:</U> <B>>=?</B>
<DD>These are equivalent to the procedures of the same name but without the
trailing `<SAMP>?</SAMP>'.
</DL>
<P>
<A NAME="Rev4 Optional Procedures"></A>
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<H3> 7.4.5 Rev4 Optional Procedures </H3>
<!--docid::SEC240::-->
<P>
<CODE>(require 'rev4-optional-procedures)</CODE>
<A NAME="IDX1446"></A>
</P>
<P>
For the specification of these optional procedures,
See section `Standard procedures' in <CITE>Revised(4) Scheme</CITE>.
</P>
<P>
<A NAME="IDX1447"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list-tail</B> <I>l p</I>
<DD></DL>
<P>
<A NAME="IDX1448"></A>
</P>
<DL>
<DT><U>Function:</U> <B>string->list</B> <I>s</I>
<DD></DL>
<P>
<A NAME="IDX1449"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list->string</B> <I>l</I>
<DD></DL>
<P>
<A NAME="IDX1450"></A>
</P>
<DL>
<DT><U>Function:</U> <B>string-copy</B>
<DD></DL>
<P>
<A NAME="IDX1451"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>string-fill!</B> <I>s obj</I>
<DD></DL>
<P>
<A NAME="IDX1452"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list->vector</B> <I>l</I>
<DD></DL>
<P>
<A NAME="IDX1453"></A>
</P>
<DL>
<DT><U>Function:</U> <B>vector->list</B> <I>s</I>
<DD></DL>
<P>
<A NAME="IDX1454"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>vector-fill!</B> <I>s obj</I>
<DD></DL>
<P>
<A NAME="Multi-argument / and -"></A>
<HR SIZE="6">
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<H3> 7.4.6 Multi-argument / and - </H3>
<!--docid::SEC241::-->
<P>
<CODE>(require 'multiarg/and-)</CODE>
<A NAME="IDX1455"></A>
</P>
<P>
For the specification of these optional forms, See section `Numerical operations' in <CITE>Revised(4) Scheme</CITE>.
</P>
<P>
<A NAME="IDX1456"></A>
</P>
<DL>
<DT><U>Function:</U> <B>/</B> <I>dividend divisor1 <small>...</small></I>
<DD></DL>
<P>
<A NAME="IDX1457"></A>
</P>
<DL>
<DT><U>Function:</U> <B>-</B> <I>minuend subtrahend1 <small>...</small></I>
<DD></DL>
<P>
<A NAME="Multi-argument Apply"></A>
<HR SIZE="6">
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<H3> 7.4.7 Multi-argument Apply </H3>
<!--docid::SEC242::-->
<P>
<CODE>(require 'multiarg-apply)</CODE>
<A NAME="IDX1458"></A>
</P>
<P>
For the specification of this optional form,
See section `Control features' in <CITE>Revised(4) Scheme</CITE>.
</P>
<P>
<A NAME="IDX1459"></A>
</P>
<DL>
<DT><U>Function:</U> <B>apply</B> <I>proc arg1 <small>...</small></I>
<DD></DL>
<P>
<A NAME="Rationalize"></A>
<HR SIZE="6">
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<H3> 7.4.8 Rationalize </H3>
<!--docid::SEC243::-->
<P>
<CODE>(require 'rationalize)</CODE>
<A NAME="IDX1460"></A>
</P>
<P>
<A NAME="IDX1461"></A>
</P>
<DL>
<DT><U>Function:</U> <B>rationalize</B> <I>x e</I>
<DD><P>
Computes the correct result for exact arguments (provided the
implementation supports exact rational numbers of unlimited precision);
and produces a reasonable answer for inexact arguments when inexact
arithmetic is implemented using floating-point.
</P>
<P>
</P>
</DL>
<CODE>Rationalize</CODE> has limited use in implementations lacking exact
(non-integer) rational numbers. The following procedures return a list
of the numerator and denominator.
<P>
<A NAME="IDX1462"></A>
</P>
<DL>
<DT><U>Function:</U> <B>find-ratio</B> <I>x e</I>
<DD><P>
<CODE>find-ratio</CODE> returns the list of the <EM>simplest</EM>
numerator and denominator whose quotient differs from <VAR>x</VAR> by no more
than <VAR>e</VAR>.
</P>
<P>
<TABLE><tr><td> </td><td class=display><pre style="font-family: serif"><TT>(find-ratio 3/97 .0001) => (3 97)
(find-ratio 3/97 .001) => (1 32)
</TT>
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1463"></A>
</P>
<DL>
<DT><U>Function:</U> <B>find-ratio-between</B> <I>x y</I>
<DD><P>
<CODE>find-ratio-between</CODE> returns the list of the <EM>simplest</EM>
numerator and denominator between <VAR>x</VAR> and <VAR>y</VAR>.
</P>
<P>
<TABLE><tr><td> </td><td class=display><pre style="font-family: serif"><TT>(find-ratio-between 2/7 3/5) => (1 2)
(find-ratio-between -3/5 -2/7) => (-1 2)
</TT>
</pre></td></tr></table></DL>
<P>
<A NAME="Promises"></A>
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<H3> 7.4.9 Promises </H3>
<!--docid::SEC244::-->
<P>
<CODE>(require 'promise)</CODE>
<A NAME="IDX1464"></A>
</P>
<P>
<A NAME="IDX1465"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-promise</B> <I>proc</I>
<DD></DL>
<P>
<A NAME="IDX1466"></A>
</P>
<DL>
<DT><U>Function:</U> <B>force</B> <I>promise</I>
<DD></DL>
<P>
<CODE>(require 'delay)</CODE> provides <CODE>force</CODE> and <CODE>delay</CODE>:
</P>
<P>
<A NAME="IDX1467"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>delay</B> <I>obj</I>
<DD>Change occurrences of <CODE>(delay <VAR>expression</VAR>)</CODE> to
<P>
<TABLE><tr><td> </td><td class=example><pre>(make-promise (lambda () <VAR>expression</VAR>))
</pre></td></tr></table><P>
</P>
</DL>
<P>
(see section `Control features' in <CITE>Revised(4) Scheme</CITE>).
</P>
<P>
<A NAME="Dynamic-Wind"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.4.10 Dynamic-Wind </H3>
<!--docid::SEC245::-->
<P>
<CODE>(require 'dynamic-wind)</CODE>
<A NAME="IDX1468"></A>
</P>
<P>
This facility is a generalization of Common LISP <CODE>unwind-protect</CODE>,
designed to take into account the fact that continuations produced by
<CODE>call-with-current-continuation</CODE> may be reentered.
</P>
<P>
<A NAME="IDX1469"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>dynamic-wind</B> <I>thunk1 thunk2 thunk3</I>
<DD>The arguments <VAR>thunk1</VAR>, <VAR>thunk2</VAR>, and <VAR>thunk3</VAR> must all be
procedures of no arguments (thunks).
<P>
<CODE>dynamic-wind</CODE> calls <VAR>thunk1</VAR>, <VAR>thunk2</VAR>, and then
<VAR>thunk3</VAR>. The value returned by <VAR>thunk2</VAR> is returned as the
result of <CODE>dynamic-wind</CODE>. <VAR>thunk3</VAR> is also called just before
control leaves the dynamic context of <VAR>thunk2</VAR> by calling a
continuation created outside that context. Furthermore, <VAR>thunk1</VAR> is
called before reentering the dynamic context of <VAR>thunk2</VAR> by calling
a continuation created inside that context. (Control is inside the
context of <VAR>thunk2</VAR> if <VAR>thunk2</VAR> is on the current return stack).
</P>
<P>
<STRONG>Warning:</STRONG> There is no provision for dealing with errors or
interrupts. If an error or interrupt occurs while using
<CODE>dynamic-wind</CODE>, the dynamic environment will be that in effect at
the time of the error or interrupt.
</P>
</DL>
<P>
<A NAME="Eval"></A>
<HR SIZE="6">
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<H3> 7.4.11 Eval </H3>
<!--docid::SEC246::-->
<P>
<CODE>(require 'eval)</CODE>
<A NAME="IDX1470"></A>
</P>
<P>
<A NAME="IDX1471"></A>
</P>
<DL>
<DT><U>Function:</U> <B>eval</B> <I>expression environment-specifier</I>
<DD><P>
Evaluates <VAR>expression</VAR> in the specified environment and returns its
value. <VAR>Expression</VAR> must be a valid Scheme expression represented
as data, and <VAR>environment-specifier</VAR> must be a value returned by one
of the three procedures described below. Implementations may extend
<CODE>eval</CODE> to allow non-expression programs (definitions) as the first
argument and to allow other values as environments, with the restriction
that <CODE>eval</CODE> is not allowed to create new bindings in the
environments associated with <CODE>null-environment</CODE> or
<CODE>scheme-report-environment</CODE>.
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(eval '(* 7 3) (scheme-report-environment 5))
=> 21
(let ((f (eval '(lambda (f x) (f x x))
(null-environment))))
(f + 10))
=> 20
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1472"></A>
</P>
<DL>
<DT><U>Function:</U> <B>scheme-report-environment</B> <I>version</I>
<DD><A NAME="IDX1473"></A>
<DT><U>Function:</U> <B>null-environment</B> <I>version</I>
<DD><A NAME="IDX1474"></A>
<DT><U>Function:</U> <B>null-environment</B>
<DD><P>
<VAR>Version</VAR> must be an exact non-negative integer <VAR>n</VAR>
corresponding to a version of one of the Revised^<VAR>n</VAR> Reports on
Scheme. <CODE>Scheme-report-environment</CODE> returns a specifier for an
environment that contains the set of bindings specified in the
corresponding report that the implementation supports.
<CODE>Null-environment</CODE> returns a specifier for an environment that
contains only the (syntactic) bindings for all the syntactic keywords
defined in the given version of the report.
</P>
<P>
Not all versions may be available in all implementations at all times.
However, an implementation that conforms to version <VAR>n</VAR> of the
Revised^<VAR>n</VAR> Reports on Scheme must accept version <VAR>n</VAR>. An error
is signalled if the specified version is not available.
</P>
<P>
The effect of assigning (through the use of <CODE>eval</CODE>) a variable
bound in a <CODE>scheme-report-environment</CODE> (for example <CODE>car</CODE>) is
unspecified. Thus the environments specified by
<CODE>scheme-report-environment</CODE> may be immutable.
</P>
<P>
</P>
</DL>
<P>
<A NAME="IDX1475"></A>
</P>
<DL>
<DT><U>Function:</U> <B>interaction-environment</B>
<DD><P>
This optional procedure returns a specifier for the environment that
contains implementation-defined bindings, typically a superset of those
listed in the report. The intent is that this procedure will return the
environment in which the implementation would evaluate expressions
dynamically typed by the user.
</P>
</DL>
<P>
Here are some more <CODE>eval</CODE> examples:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(require 'eval)
=> #<unspecified>
(define car 'volvo)
=> #<unspecified>
car
=> volvo
(eval 'car (interaction-environment))
=> volvo
(eval 'car (scheme-report-environment 5))
=> #<primitive-procedure car>
(eval '(eval 'car (interaction-environment))
(scheme-report-environment 5))
=> volvo
(eval '(eval '(set! car 'buick) (interaction-environment))
(scheme-report-environment 5))
=> #<unspecified>
car
=> buick
(eval 'car (scheme-report-environment 5))
=> #<primitive-procedure car>
(eval '(eval 'car (interaction-environment))
(scheme-report-environment 5))
=> buick
</pre></td></tr></table><P>
<A NAME="Values"></A>
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<H3> 7.4.12 Values </H3>
<!--docid::SEC247::-->
<P>
<CODE>(require 'values)</CODE>
<A NAME="IDX1476"></A>
</P>
<P>
<A NAME="IDX1477"></A>
</P>
<DL>
<DT><U>Function:</U> <B>values</B> <I>obj <small>...</small></I>
<DD><CODE>values</CODE> takes any number of arguments, and passes (returns) them
to its continuation.
</DL>
<P>
<A NAME="IDX1478"></A>
</P>
<DL>
<DT><U>Function:</U> <B>call-with-values</B> <I>thunk proc</I>
<DD><VAR>thunk</VAR> must be a procedure of no arguments, and <VAR>proc</VAR> must be
a procedure. <CODE>call-with-values</CODE> calls <VAR>thunk</VAR> with a
continuation that, when passed some values, calls <VAR>proc</VAR> with those
values as arguments.
<P>
Except for continuations created by the <CODE>call-with-values</CODE>
procedure, all continuations take exactly one value, as now; the effect
of passing no value or more than one value to continuations that were
not created by the <CODE>call-with-values</CODE> procedure is
unspecified.
</P>
</DL>
<P>
<A NAME="SRFI"></A>
<HR SIZE="6">
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<H3> 7.4.13 SRFI </H3>
<!--docid::SEC248::-->
<P>
<CODE>(require 'srfi)</CODE>
<A NAME="IDX1479"></A>
</P>
<P>
Implements <EM>Scheme Request For Implementation</EM> (SRFI) as
<A NAME="IDX1480"></A>
described at <A HREF="http://srfi.schemers.org/">http://srfi.schemers.org/</A>
</P>
<P>
The Copyright terms of each SRFI states:
<BLOCKQUOTE>
"However, this document itself may not be modified in any way, ..."
</BLOCKQUOTE>
<P>
Therefore, the specification of SRFI constructs must not be
quoted without including the complete SRFI document containing
discussion and a sample implementation program.
</P>
<P>
<A NAME="IDX1481"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>cond-expand</B> <I><clause1> <clause2> <small>...</small></I>
<DD><P>
<EM>Syntax:</EM>
Each <clause> should be of the form
</P>
<P>
<TABLE><tr><td> </td><td class=display><pre style="font-family: serif"><TT>(<feature> <expression1> <small>...</small>)</TT>
</pre></td></tr></table><P>
where <feature> is a boolean expression composed of symbols and
`and', `or', and `not' of boolean expressions. The last <clause>
may be an "else clause," which has the form
</P>
<P>
<TABLE><tr><td> </td><td class=display><pre style="font-family: serif"><TT>(else <expression1> <expression2> <small>...</small>).</TT>
</pre></td></tr></table><P>
The first clause whose feature expression is satisfied is expanded.
If no feature expression is satisfied and there is no else clause, an
error is signaled.
</P>
<P>
SLIB <CODE>cond-expand</CODE> is an extension of SRFI-0,
<A HREF="http://srfi.schemers.org/srfi-0/srfi-0.html">http://srfi.schemers.org/srfi-0/srfi-0.html</A>.
</P>
</DL>
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC249">7.4.13.1 SRFI-1</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">list-processing</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC260">7.4.13.2 SRFI-2</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">guarded LET* special form</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC261">7.4.13.3 SRFI-8</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Binding to multiple values</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC262">7.4.13.4 SRFI-9</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Defining Record Types</TD></TR>
</TABLE>
<P>
<A NAME="SRFI-1"></A>
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<H4> 7.4.13.1 SRFI-1 </H4>
<!--docid::SEC249::-->
<P>
<CODE>(require 'srfi-1)</CODE>
<A NAME="IDX1482"></A>
</P>
<P>
Implements the <EM>SRFI-1</EM> <EM>list-processing library</EM> as described
<A NAME="IDX1483"></A>
<A NAME="IDX1484"></A>
at <A HREF="http://srfi.schemers.org/srfi-1/srfi-1.html">http://srfi.schemers.org/srfi-1/srfi-1.html</A>
</P>
<P>
<A NAME="SEC250"></A>
<H3> Constructors </H3>
<!--docid::SEC250::-->
<P>
<A NAME="IDX1485"></A>
</P>
<DL>
<DT><U>Function:</U> <B>xcons</B> <I>d a</I>
<DD><CODE>(define (xcons d a) (cons a d))</CODE>.
</DL>
<P>
<A NAME="IDX1486"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list-tabulate</B> <I>len proc</I>
<DD>Returns a list of length <VAR>len</VAR>. Element <VAR>i</VAR> is <CODE>(<VAR>proc</VAR>
<VAR>i</VAR>)</CODE> for 0 <= <VAR>i</VAR> < <VAR>len</VAR>.
</DL>
<P>
<A NAME="IDX1487"></A>
</P>
<DL>
<DT><U>Function:</U> <B>cons*</B> <I>obj1 obj2</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1488"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list-copy</B> <I>flist</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1489"></A>
</P>
<DL>
<DT><U>Function:</U> <B>iota</B> <I>count start step</I>
<DD><P>
<A NAME="IDX1490"></A>
<DT><U>Function:</U> <B>iota</B> <I>count start</I>
<DD></P>
<P>
<A NAME="IDX1491"></A>
<DT><U>Function:</U> <B>iota</B> <I>count</I>
<DD>Returns a list of <VAR>count</VAR> numbers: (<VAR>start</VAR>, <VAR>start</VAR>+<VAR>step</VAR>, <small>...</small>, <VAR>start</VAR>+(<VAR>count</VAR>-1)*<VAR>step</VAR>).
</P>
</DL>
<P>
<A NAME="IDX1492"></A>
</P>
<DL>
<DT><U>Function:</U> <B>circular-list</B> <I>obj1 obj2 <small>...</small></I>
<DD><P>
Returns a circular list of <VAR>obj1</VAR>, <VAR>obj2</VAR>, <small>...</small>.
</P>
</DL>
<A NAME="SEC251"></A>
<H3> Predicates </H3>
<!--docid::SEC251::-->
<P>
<A NAME="IDX1493"></A>
</P>
<DL>
<DT><U>Function:</U> <B>proper-list?</B> <I>obj</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1494"></A>
</P>
<DL>
<DT><U>Function:</U> <B>circular-list?</B> <I>x</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1495"></A>
</P>
<DL>
<DT><U>Function:</U> <B>dotted-list?</B> <I>obj</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1496"></A>
</P>
<DL>
<DT><U>Function:</U> <B>null-list?</B> <I>obj</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1497"></A>
</P>
<DL>
<DT><U>Function:</U> <B>not-pair?</B> <I>obj</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1498"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list=</B> <I>=pred list <small>...</small></I>
<DD><P>
</P>
</DL>
<A NAME="SEC252"></A>
<H3> Selectors </H3>
<!--docid::SEC252::-->
<P>
<A NAME="IDX1499"></A>
</P>
<DL>
<DT><U>Function:</U> <B>first</B> <I>pair</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1500"></A>
</P>
<DL>
<DT><U>Function:</U> <B>second</B> <I>pair</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1501"></A>
</P>
<DL>
<DT><U>Function:</U> <B>third</B> <I>pair</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1502"></A>
</P>
<DL>
<DT><U>Function:</U> <B>fourth</B> <I>pair</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1503"></A>
</P>
<DL>
<DT><U>Function:</U> <B>fifth</B> <I>pair</I>
<DD><A NAME="IDX1504"></A>
<DT><U>Function:</U> <B>sixth</B> <I>obj</I>
<DD><A NAME="IDX1505"></A>
<DT><U>Function:</U> <B>seventh</B> <I>obj</I>
<DD><A NAME="IDX1506"></A>
<DT><U>Function:</U> <B>eighth</B> <I>obj</I>
<DD><A NAME="IDX1507"></A>
<DT><U>Function:</U> <B>ninth</B> <I>obj</I>
<DD><A NAME="IDX1508"></A>
<DT><U>Function:</U> <B>tenth</B> <I>obj</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1509"></A>
</P>
<DL>
<DT><U>Function:</U> <B>car+cdr</B> <I>pair</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1510"></A>
</P>
<DL>
<DT><U>Function:</U> <B>drop</B> <I>lst k</I>
<DD><A NAME="IDX1511"></A>
<DT><U>Function:</U> <B>take</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1512"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>take!</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1513"></A>
</P>
<DL>
<DT><U>Function:</U> <B>take-right</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1514"></A>
</P>
<DL>
<DT><U>Function:</U> <B>drop-right</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1515"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>drop-right!</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1516"></A>
</P>
<DL>
<DT><U>Function:</U> <B>split-at</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1517"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>split-at!</B> <I>lst k</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1518"></A>
</P>
<DL>
<DT><U>Function:</U> <B>last</B> <I>lst</I>
<DD><P>
(car (last-pair lst))
</P>
</DL>
<A NAME="SEC253"></A>
<H3> Miscellaneous </H3>
<!--docid::SEC253::-->
<P>
<A NAME="IDX1519"></A>
</P>
<DL>
<DT><U>Function:</U> <B>length+</B> <I>obj</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1520"></A>
</P>
<DL>
<DT><U>Function:</U> <B>concatenate</B> <I>lists</I>
<DD><A NAME="IDX1521"></A>
<DT><U>Function:</U> <B>concatenate!</B> <I>lists</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1522"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>reverse!</B> <I>lst</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1523"></A>
</P>
<DL>
<DT><U>Function:</U> <B>append-reverse</B> <I>rev-head tail</I>
<DD><A NAME="IDX1524"></A>
<DT><U>Function:</U> <B>append-reverse!</B> <I>rev-head tail</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1525"></A>
</P>
<DL>
<DT><U>Function:</U> <B>zip</B> <I>list1 list2 <small>...</small></I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1526"></A>
</P>
<DL>
<DT><U>Function:</U> <B>unzip1</B> <I>lst</I>
<DD><A NAME="IDX1527"></A>
<DT><U>Function:</U> <B>unzip2</B> <I>lst</I>
<DD><A NAME="IDX1528"></A>
<DT><U>Function:</U> <B>unzip3</B> <I>lst</I>
<DD><A NAME="IDX1529"></A>
<DT><U>Function:</U> <B>unzip4</B> <I>lst</I>
<DD><A NAME="IDX1530"></A>
<DT><U>Function:</U> <B>unzip5</B> <I>lst</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1531"></A>
</P>
<DL>
<DT><U>Function:</U> <B>count</B> <I>pred list1 list2 <small>...</small></I>
<DD><P>
</P>
</DL>
<A NAME="SEC254"></A>
<H3> Fold and Unfold </H3>
<!--docid::SEC254::-->
<P>
<A NAME="IDX1532"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>map!</B> <I>f list1 clist2 <small>...</small></I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1533"></A>
</P>
<DL>
<DT><U>Function:</U> <B>pair-for-each</B> <I>f clist1 clist2 <small>...</small></I>
<DD><P>
</P>
</DL>
<A NAME="SEC255"></A>
<H3> Filtering and Partitioning </H3>
<!--docid::SEC255::-->
<P>
<A NAME="IDX1534"></A>
</P>
<DL>
<DT><U>Function:</U> <B>filter</B> <I>pred lis</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1535"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>filter!</B> <I>pred l</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1536"></A>
</P>
<DL>
<DT><U>Function:</U> <B>partition</B> <I>pred list</I>
<DD><P>
</P>
</DL>
<A NAME="SEC256"></A>
<H3> Searching </H3>
<!--docid::SEC256::-->
<P>
<A NAME="IDX1537"></A>
</P>
<DL>
<DT><U>Function:</U> <B>find</B> <I>pred list</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1538"></A>
</P>
<DL>
<DT><U>Function:</U> <B>find-tail</B> <I>pred list</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1539"></A>
</P>
<DL>
<DT><U>Function:</U> <B>remove</B> <I>pred l</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1540"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>remove!</B> <I>pred l</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1541"></A>
</P>
<DL>
<DT><U>Function:</U> <B>any</B> <I>pred clist1 clist2 <small>...</small></I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1542"></A>
</P>
<DL>
<DT><U>Function:</U> <B>list-index</B> <I>pred clist1 clist2 <small>...</small></I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1543"></A>
</P>
<DL>
<DT><U>Function:</U> <B>span</B> <I>pred list</I>
<DD><P>
</P>
</DL>
<P>
<A NAME="IDX1544"></A>
</P>
<DL>
<DT><U>Function:</U> <B>member</B> <I>obj list pred</I>
<DD><P>
<A NAME="IDX1545"></A>
<DT><U>Function:</U> <B>member</B> <I>obj list</I>
<DD></P>
<P>
<CODE>member</CODE> returns the first sublist of <VAR>list</VAR> whose car is <VAR>obj</VAR>, where the sublists
of <VAR>list</VAR> are the non-empty lists returned by <TT>(list-tail <VAR>list</VAR> <VAR>k</VAR>)</TT>
for <VAR>k</VAR> less than the length of <VAR>list</VAR>. If <VAR>obj</VAR> does not occur in <VAR>list</VAR>,
then <TT>#f</TT> (not the empty list) is returned. The procedure <VAR>pred</VAR> is
used for testing equality. If <VAR>pred</VAR> is not provided, `<SAMP>equal?</SAMP>' is
used.
</P>
</DL>
<A NAME="SEC257"></A>
<H3> Deleting </H3>
<!--docid::SEC257::-->
<P>
<A NAME="SEC258"></A>
<H3> Association lists </H3>
<!--docid::SEC258::-->
<P>
<A NAME="IDX1546"></A>
</P>
<DL>
<DT><U>Function:</U> <B>assoc</B> <I>obj alist pred</I>
<DD><P>
<A NAME="IDX1547"></A>
<DT><U>Function:</U> <B>assoc</B> <I>obj alist</I>
<DD></P>
<P>
<VAR>alist</VAR> (for "association list") must be a list of pairs. These
procedures find the first pair in <VAR>alist</VAR> whose car field is <VAR>obj</VAR>, and
returns that pair. If no pair in <VAR>alist</VAR> has <VAR>obj</VAR> as its car, then <TT>#f</TT>
(not the empty list) is returned. The procedure <VAR>pred</VAR> is used for
testing equality. If <VAR>pred</VAR> is not provided, `<SAMP>equal?</SAMP>' is used.
</P>
</DL>
<A NAME="SEC259"></A>
<H3> Set operations </H3>
<!--docid::SEC259::-->
<P>
<A NAME="SRFI-2"></A>
<HR SIZE="6">
<A NAME="SEC260"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC249"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC261"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC183"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC248"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_8.html#SEC277"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H4> 7.4.13.2 SRFI-2 </H4>
<!--docid::SEC260::-->
<P>
<CODE>(require 'srfi-2)</CODE>
<A NAME="IDX1548"></A>
</P>
<P>
<A NAME="IDX1549"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>and-let*</B> <I>claws body <small>...</small></I>
<DD><P>
<A HREF="http://srfi.schemers.org/srfi-2/srfi-2.html">http://srfi.schemers.org/srfi-2/srfi-2.html</A>
</P>
</DL>
<P>
<A NAME="SRFI-8"></A>
<HR SIZE="6">
<A NAME="SEC261"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC260"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC262"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC183"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC248"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_8.html#SEC277"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H4> 7.4.13.3 SRFI-8 </H4>
<!--docid::SEC261::-->
<P>
<CODE>(require 'srfi-8)</CODE>
<A NAME="IDX1550"></A>
</P>
<P>
<A NAME="IDX1551"></A>
</P>
<DL>
<DT><U>Special Form:</U> <B>receive</B> <I>formals expression body <small>...</small></I>
<DD><P>
<A HREF="http://srfi.schemers.org/srfi-8/srfi-8.html">http://srfi.schemers.org/srfi-8/srfi-8.html</A>
</P>
</DL>
<P>
<A NAME="SRFI-9"></A>
<HR SIZE="6">
<A NAME="SEC262"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC261"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC263"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC183"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC248"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_8.html#SEC277"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H4> 7.4.13.4 SRFI-9 </H4>
<!--docid::SEC262::-->
<P>
<CODE>(require 'srfi-9)</CODE>
<A NAME="IDX1552"></A>
</P>
<P>
<A HREF="http://srfi.schemers.org/srfi-9/srfi-9.html">http://srfi.schemers.org/srfi-9/srfi-9.html</A>
</P>
<P>
<A NAME="IDX1553"></A>
</P>
<DL>
<DT><U>Special Form:</U> <B>define-record-type</B> <I><type-name> (<constructor-name> <field-tag> ...) <predicate-name> <field spec> ...</I>
<DD><P>
Where
<TABLE><tr><td> </td><td class=example><pre><field-spec> == (<field-tag> <accessor-name>)
== (<field-tag> <accessor-name> <modifier-name>)
</pre></td></tr></table><P>
<CODE>define-record-type</CODE> is a syntax wrapper for the SLIB
<CODE>record</CODE> module.
</P>
</DL>
<P>
<A NAME="Session Support"></A>
<HR SIZE="6">
<A NAME="SEC263"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC262"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC264"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC183"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC183"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_8.html#SEC277"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 7.5 Session Support </H2>
<!--docid::SEC263::-->
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC264">7.5.1 Repl</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Macros at top-level</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC265">7.5.2 Quick Print</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Loop-safe Output</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC266">7.5.3 Debug</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">To err is human ...</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC267">7.5.4 Breakpoints</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Pause execution</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC268">7.5.5 Tracing</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">'trace</TD></TR>
</TABLE>
<P>
<A NAME="Repl"></A>
<HR SIZE="6">
<A NAME="SEC264"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC263"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC265"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC183"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_7.html#SEC263"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_8.html#SEC277"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H3> 7.5.1 Repl </H3>
<!--docid::SEC264::-->
<P>
<CODE>(require 'repl)</CODE>
<A NAME="IDX1554"></A>
</P>
<P>
Here is a read-eval-print-loop which, given an eval, evaluates forms.
</P>
<P>
<A NAME="IDX1555"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>repl:top-level</B> <I>repl:eval</I>
<DD><CODE>read</CODE>s, <CODE>repl:eval</CODE>s and <CODE>write</CODE>s expressions from
<CODE>(current-input-port)</CODE> to <CODE>(current-output-port)</CODE> until an
end-of-file is encountered. <CODE>load</CODE>, <CODE>slib:eval</CODE>,
<CODE>slib:error</CODE>, and <CODE>repl:quit</CODE> dynamically bound during
<CODE>repl:top-level</CODE>.
</DL>
<P>
<A NAME="IDX1556"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>repl:quit</B>
<DD>Exits from the invocation of <CODE>repl:top-level</CODE>.
</DL>
<P>
The <CODE>repl:</CODE> procedures establish, as much as is possible to do
portably, a top level environment supporting macros.
<CODE>repl:top-level</CODE> uses <CODE>dynamic-wind</CODE> to catch error conditions
and interrupts. If your implementation supports this you are all set.
</P>
<P>
Otherwise, if there is some way your implementation can catch error
conditions and interrupts, then have them call <CODE>slib:error</CODE>. It
will display its arguments and reenter <CODE>repl:top-level</CODE>.
<CODE>slib:error</CODE> dynamically bound by <CODE>repl:top-level</CODE>.
</P>
<P>
To have your top level loop always use macros, add any interrupt
catching lines and the following lines to your Scheme init file:
<TABLE><tr><td> </td><td class=example><pre>(require 'macro)
<A NAME="IDX1557"></A>(require 'repl)
<A NAME="IDX1558"></A>(repl:top-level macro:eval)
</pre></td></tr></table><P>
<A NAME="Quick Print"></A>
<HR SIZE="6">
<A NAME="SEC265"></A>
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<H3> 7.5.2 Quick Print </H3>
<!--docid::SEC265::-->
<P>
<CODE>(require 'qp)</CODE>
<A NAME="IDX1559"></A>
</P>
<P>
When displaying error messages and warnings, it is paramount that the
output generated for circular lists and large data structures be
limited. This section supplies a procedure to do this. It could be
much improved.
</P>
<P>
<BLOCKQUOTE>
Notice that the neccessity for truncating output eliminates
Common-Lisp's <A HREF="slib_4.html#SEC53">4.2 Format (version 3.0)</A> from consideration; even when variables
<CODE>*print-level*</CODE> and <CODE>*print-level*</CODE> are set, huge strings and
bit-vectors are <EM>not</EM> limited.
</BLOCKQUOTE>
<P>
<A NAME="IDX1560"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>qp</B> <I>arg1 <small>...</small></I>
<DD><A NAME="IDX1561"></A>
<DT><U>Procedure:</U> <B>qpn</B> <I>arg1 <small>...</small></I>
<DD><A NAME="IDX1562"></A>
<DT><U>Procedure:</U> <B>qpr</B> <I>arg1 <small>...</small></I>
<DD><CODE>qp</CODE> writes its arguments, separated by spaces, to
<CODE>(current-output-port)</CODE>. <CODE>qp</CODE> compresses printing by
substituting `<SAMP>...</SAMP>' for substructure it does not have sufficient
room to print. <CODE>qpn</CODE> is like <CODE>qp</CODE> but outputs a newline
before returning. <CODE>qpr</CODE> is like <CODE>qpn</CODE> except that it returns
its last argument.
</DL>
<P>
<A NAME="IDX1563"></A>
</P>
<DL>
<DT><U>Variable:</U> <B>*qp-width*</B>
<DD><VAR>*qp-width*</VAR> is the largest number of characters that <CODE>qp</CODE>
should use. If <VAR>*qp-width*</VAR> is #f, then all items will be
<CODE>write</CODE>n. If <VAR>*qp-width*</VAR> is 0, then all items except
procedures will be <CODE>write</CODE>n; procedures will be indicated by
`<SAMP>#[proc]</SAMP>'.
</DL>
<P>
<A NAME="Debug"></A>
<HR SIZE="6">
<A NAME="SEC266"></A>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H3> 7.5.3 Debug </H3>
<!--docid::SEC266::-->
<P>
<CODE>(require 'debug)</CODE>
<A NAME="IDX1564"></A>
</P>
<P>
Requiring <CODE>debug</CODE> automatically requires <CODE>trace</CODE> and
<CODE>break</CODE>.
</P>
<P>
An application with its own datatypes may want to substitute its own
printer for <CODE>qp</CODE>. This example shows how to do this:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(define qpn (lambda args) <small>...</small>)
(provide 'qp)
(require 'debug)
<A NAME="IDX1565"></A></pre></td></tr></table><P>
<A NAME="IDX1566"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>trace-all</B> <I>file <small>...</small></I>
<DD>Traces (see section <A HREF="slib_7.html#SEC268">7.5.5 Tracing</A>) all procedures <CODE>define</CODE>d at top-level in
`<TT>file</TT>' <small>...</small>.
<P>
<A NAME="IDX1567"></A>
<DT><U>Procedure:</U> <B>track-all</B> <I>file <small>...</small></I>
<DD>Tracks (see section <A HREF="slib_7.html#SEC268">7.5.5 Tracing</A>) all procedures <CODE>define</CODE>d at top-level in
`<TT>file</TT>' <small>...</small>.
</P>
<P>
<A NAME="IDX1568"></A>
<DT><U>Procedure:</U> <B>stack-all</B> <I>file <small>...</small></I>
<DD>Stacks (see section <A HREF="slib_7.html#SEC268">7.5.5 Tracing</A>) all procedures <CODE>define</CODE>d at top-level in
`<TT>file</TT>' <small>...</small>.
</P>
</DL>
<P>
<A NAME="IDX1569"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>break-all</B> <I>file <small>...</small></I>
<DD>Breakpoints (see section <A HREF="slib_7.html#SEC267">7.5.4 Breakpoints</A>) all procedures <CODE>define</CODE>d at
top-level in `<TT>file</TT>' <small>...</small>.
</DL>
<P>
<A NAME="Breakpoints"></A>
<HR SIZE="6">
<A NAME="SEC267"></A>
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</TR></TABLE>
<H3> 7.5.4 Breakpoints </H3>
<!--docid::SEC267::-->
<P>
<CODE>(require 'break)</CODE>
<A NAME="IDX1570"></A>
</P>
<P>
<A NAME="IDX1571"></A>
</P>
<DL>
<DT><U>Function:</U> <B>init-debug</B>
<DD>If your Scheme implementation does not support <CODE>break</CODE> or
<CODE>abort</CODE>, a message will appear when you <CODE>(require 'break)</CODE> or
<A NAME="IDX1572"></A>
<CODE>(require 'debug)</CODE> telling you to type <CODE>(init-debug)</CODE>. This
<A NAME="IDX1573"></A>
is in order to establish a top-level continuation. Typing
<CODE>(init-debug)</CODE> at top level sets up a continuation for
<CODE>break</CODE>.
</DL>
<P>
<A NAME="IDX1574"></A>
</P>
<DL>
<DT><U>Function:</U> <B>breakpoint</B> <I>arg1 <small>...</small></I>
<DD>Returns from the top level continuation and pushes the continuation from
which it was called on a continuation stack.
</DL>
<P>
<A NAME="IDX1575"></A>
</P>
<DL>
<DT><U>Function:</U> <B>continue</B>
<DD>Pops the topmost continuation off of the continuation stack and returns
an unspecified value to it.
<P>
<A NAME="IDX1576"></A>
<DT><U>Function:</U> <B>continue</B> <I>arg1 <small>...</small></I>
<DD>Pops the topmost continuation off of the continuation stack and returns
<VAR>arg1</VAR> <small>...</small> to it.
</P>
</DL>
<P>
<A NAME="IDX1577"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>break</B> <I>proc1 <small>...</small></I>
<DD>Redefines the top-level named procedures given as arguments so that
<CODE>breakpoint</CODE> is called before calling <VAR>proc1</VAR> <small>...</small>.
<A NAME="IDX1578"></A>
<DT><U>Macro:</U> <B>break</B>
<DD>With no arguments, makes sure that all the currently broken identifiers
are broken (even if those identifiers have been redefined) and returns a
list of the broken identifiers.
</DL>
<P>
<A NAME="IDX1579"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>unbreak</B> <I>proc1 <small>...</small></I>
<DD>Turns breakpoints off for its arguments.
<A NAME="IDX1580"></A>
<DT><U>Macro:</U> <B>unbreak</B>
<DD>With no arguments, unbreaks all currently broken identifiers and returns
a list of these formerly broken identifiers.
</DL>
<P>
These are <EM>procedures</EM> for breaking. If defmacros are not natively
supported by your implementation, these might be more convenient to use.
</P>
<P>
<A NAME="IDX1581"></A>
</P>
<DL>
<DT><U>Function:</U> <B>breakf</B> <I>proc</I>
<DD><A NAME="IDX1582"></A>
<DT><U>Function:</U> <B>breakf</B> <I>proc name</I>
<DD>To break, type
<TABLE><tr><td> </td><td class=example><pre>(set! <VAR>symbol</VAR> (breakf <VAR>symbol</VAR>))
</pre></td></tr></table>or
<TABLE><tr><td> </td><td class=example><pre>(set! <VAR>symbol</VAR> (breakf <VAR>symbol</VAR> '<VAR>symbol</VAR>))
</pre></td></tr></table>or
<TABLE><tr><td> </td><td class=example><pre>(define <VAR>symbol</VAR> (breakf <VAR>function</VAR>))
</pre></td></tr></table>or
<TABLE><tr><td> </td><td class=example><pre>(define <VAR>symbol</VAR> (breakf <VAR>function</VAR> '<VAR>symbol</VAR>))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1583"></A>
</P>
<DL>
<DT><U>Function:</U> <B>unbreakf</B> <I>proc</I>
<DD>To unbreak, type
<TABLE><tr><td> </td><td class=example><pre>(set! <VAR>symbol</VAR> (unbreakf <VAR>symbol</VAR>))
</pre></td></tr></table></DL>
<P>
<A NAME="Trace"></A>
<HR SIZE="6">
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</TR></TABLE>
<H3> 7.5.5 Tracing </H3>
<!--docid::SEC268::-->
<P>
<CODE>(require 'trace)</CODE>
<A NAME="IDX1584"></A>
</P>
<P>
This feature provides three ways to monitor procedure invocations:
</P>
<P>
</P>
<DL COMPACT>
<DT>stack
<DD>Pushes the procedure-name when the procedure is called; pops when it
returns.
<DT>track
<DD>Pushes the procedure-name and arguments when the procedure is called;
pops when it returns.
<DT>trace
<DD>Pushes the procedure-name and prints `<SAMP>CALL <VAR>procedure-name</VAR>
<VAR>arg1</VAR> <small>...</small></SAMP>' when the procdure is called; pops and prints
`<SAMP>RETN <VAR>procedure-name</VAR> <VAR>value</VAR></SAMP>' when the procedure returns.
</DL>
<P>
<A NAME="IDX1585"></A>
</P>
<DL>
<DT><U>Variable:</U> <B>debug:max-count</B>
<DD>If a traced procedure calls itself or untraced procedures which call it,
stack, track, and trace will limit the number of stack pushes to
<VAR>debug:max-count</VAR>.
</DL>
<P>
<A NAME="IDX1586"></A>
</P>
<DL>
<DT><U>Function:</U> <B>print-call-stack</B>
<DD><A NAME="IDX1587"></A>
<DT><U>Function:</U> <B>print-call-stack</B> <I>port</I>
<DD>Prints the call-stack to <VAR>port</VAR> or the current-error-port.
</DL>
<P>
<A NAME="IDX1588"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>trace</B> <I>proc1 <small>...</small></I>
<DD>Traces the top-level named procedures given as arguments.
<A NAME="IDX1589"></A>
<DT><U>Macro:</U> <B>trace</B>
<DD>With no arguments, makes sure that all the currently traced identifiers
are traced (even if those identifiers have been redefined) and returns a
list of the traced identifiers.
</DL>
<P>
<A NAME="IDX1590"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>track</B> <I>proc1 <small>...</small></I>
<DD>Traces the top-level named procedures given as arguments.
<A NAME="IDX1591"></A>
<DT><U>Macro:</U> <B>track</B>
<DD>With no arguments, makes sure that all the currently tracked identifiers
are tracked (even if those identifiers have been redefined) and returns
a list of the tracked identifiers.
</DL>
<P>
<A NAME="IDX1592"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>stack</B> <I>proc1 <small>...</small></I>
<DD>Traces the top-level named procedures given as arguments.
<A NAME="IDX1593"></A>
<DT><U>Macro:</U> <B>stack</B>
<DD>With no arguments, makes sure that all the currently stacked identifiers
are stacked (even if those identifiers have been redefined) and returns
a list of the stacked identifiers.
</DL>
<P>
<A NAME="IDX1594"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>untrace</B> <I>proc1 <small>...</small></I>
<DD>Turns tracing, tracking, and off for its arguments.
<A NAME="IDX1595"></A>
<DT><U>Macro:</U> <B>untrace</B>
<DD>With no arguments, untraces all currently traced identifiers and returns
a list of these formerly traced identifiers.
</DL>
<P>
<A NAME="IDX1596"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>untrack</B> <I>proc1 <small>...</small></I>
<DD>Turns tracing, tracking, and off for its arguments.
<A NAME="IDX1597"></A>
<DT><U>Macro:</U> <B>untrack</B>
<DD>With no arguments, untracks all currently tracked identifiers and returns
a list of these formerly tracked identifiers.
</DL>
<P>
<A NAME="IDX1598"></A>
</P>
<DL>
<DT><U>Macro:</U> <B>unstack</B> <I>proc1 <small>...</small></I>
<DD>Turns tracing, stacking, and off for its arguments.
<A NAME="IDX1599"></A>
<DT><U>Macro:</U> <B>unstack</B>
<DD>With no arguments, unstacks all currently stacked identifiers and returns
a list of these formerly stacked identifiers.
</DL>
<P>
These are <EM>procedures</EM> for tracing. If defmacros are not natively
supported by your implementation, these might be more convenient to use.
</P>
<P>
<A NAME="IDX1600"></A>
</P>
<DL>
<DT><U>Function:</U> <B>tracef</B> <I>proc</I>
<DD><A NAME="IDX1601"></A>
<DT><U>Function:</U> <B>tracef</B> <I>proc name</I>
<DD><A NAME="IDX1602"></A>
<DT><U>Function:</U> <B>trackf</B> <I>proc</I>
<DD><A NAME="IDX1603"></A>
<DT><U>Function:</U> <B>trackf</B> <I>proc name</I>
<DD><A NAME="IDX1604"></A>
<DT><U>Function:</U> <B>stackf</B> <I>proc</I>
<DD><A NAME="IDX1605"></A>
<DT><U>Function:</U> <B>stackf</B> <I>proc name</I>
<DD>To trace, type
<TABLE><tr><td> </td><td class=example><pre>(set! <VAR>symbol</VAR> (tracef <VAR>symbol</VAR>))
</pre></td></tr></table>or
<TABLE><tr><td> </td><td class=example><pre>(set! <VAR>symbol</VAR> (tracef <VAR>symbol</VAR> '<VAR>symbol</VAR>))
</pre></td></tr></table>or
<TABLE><tr><td> </td><td class=example><pre>(define <VAR>symbol</VAR> (tracef <VAR>function</VAR>))
</pre></td></tr></table>or
<TABLE><tr><td> </td><td class=example><pre>(define <VAR>symbol</VAR> (tracef <VAR>function</VAR> '<VAR>symbol</VAR>))
</pre></td></tr></table></DL>
<P>
<A NAME="IDX1606"></A>
</P>
<DL>
<DT><U>Function:</U> <B>untracef</B> <I>proc</I>
<DD>Removes tracing, tracking, or stacking for <VAR>proc</VAR>.
To untrace, type
<TABLE><tr><td> </td><td class=example><pre>(set! <VAR>symbol</VAR> (untracef <VAR>symbol</VAR>))
</pre></td></tr></table></DL>
<P>
<A NAME="System Interface"></A>
<HR SIZE="6">
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<H2> 7.6 System Interface </H2>
<!--docid::SEC269::-->
<P>
If <CODE>(provided? 'getenv)</CODE>:
</P>
<P>
<A NAME="IDX1607"></A>
</P>
<DL>
<DT><U>Function:</U> <B>getenv</B> <I>name</I>
<DD>Looks up <VAR>name</VAR>, a string, in the program environment. If <VAR>name</VAR> is
found a string of its value is returned. Otherwise, <CODE>#f</CODE> is returned.
</DL>
<P>
If <CODE>(provided? 'system)</CODE>:
</P>
<P>
<A NAME="IDX1608"></A>
</P>
<DL>
<DT><U>Function:</U> <B>system</B> <I>command-string</I>
<DD>Executes the <VAR>command-string</VAR> on the computer and returns the
integer status code.
</DL>
<P>
<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC270">7.6.1 Directories</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC271">7.6.2 Transactions</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_7.html#SEC275">7.6.3 CVS</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
</TABLE>
<P>
<A NAME="Directories"></A>
<HR SIZE="6">
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<H3> 7.6.1 Directories </H3>
<!--docid::SEC270::-->
<P>
<CODE>(require 'directory)</CODE>
<A NAME="IDX1609"></A>
</P>
<P>
<A NAME="IDX1610"></A>
</P>
<DL>
<DT><U>Function:</U> <B>current-directory</B>
<DD><P>
<CODE>current-directory</CODE> returns a string containing the absolute file
name representing the current working directory. If this string
cannot be obtained, #f is returned.
</P>
<P>
If <CODE>current-directory</CODE> cannot be supported by the platform, then #f is returned.
</P>
</DL>
<P>
<A NAME="IDX1611"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-directory</B> <I>name</I>
<DD><P>
Creates a sub-directory <VAR>name</VAR> of the current-directory. If
successful, <CODE>make-directory</CODE> returns #t; otherwise #f.
</P>
</DL>
<P>
<A NAME="IDX1612"></A>
</P>
<DL>
<DT><U>Function:</U> <B>directory-for-each</B> <I>proc directory</I>
<DD><P>
<VAR>proc</VAR> must be a procedure taking one argument.
`<SAMP>Directory-For-Each</SAMP>' applies <VAR>proc</VAR> to the (string) name of
each file in <VAR>directory</VAR>. The dynamic order in which <VAR>proc</VAR> is
applied to the filenames is unspecified. The value returned by
`<SAMP>directory-for-each</SAMP>' is unspecified.
</P>
<P>
<A NAME="IDX1613"></A>
<DT><U>Function:</U> <B>directory-for-each</B> <I>proc directory pred</I>
<DD>Applies <VAR>proc</VAR> only to those filenames for which the procedure
<VAR>pred</VAR> returns a non-false value.
</P>
<P>
<A NAME="IDX1614"></A>
<DT><U>Function:</U> <B>directory-for-each</B> <I>proc directory match</I>
<DD>Applies <VAR>proc</VAR> only to those filenames for which
<CODE>(filename:match?? <VAR>match</VAR>)</CODE> would return a non-false value
(see section `Filenames' in <CITE>SLIB</CITE>).
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>(require 'directory)
(directory-for-each print "." "[A-Z]*.scm")
-|
"Bev2slib.scm"
"Template.scm"
</pre></td></tr></table></DL>
<P>
<A NAME="Transactions"></A>
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<H3> 7.6.2 Transactions </H3>
<!--docid::SEC271::-->
<P>
If <CODE>system</CODE> is provided by the Scheme implementation, the
<EM>transact</EM> package provides functions for file-locking and
file-replacement transactions.
</P>
<P>
<CODE>(require 'transact)</CODE>
<A NAME="IDX1615"></A>
</P>
<P>
<A NAME="SEC272"></A>
<H4> File Locking </H4>
<!--docid::SEC272::-->
<P>
Unix file-locking is focussed on write permissions for segments of a
existing file. While this might be employed for (binary) database
access, it is not used for everyday contention (between users) for
text files.
</P>
<P>
Microsoft has several file-locking protocols. Their model denies
write access to a file if any reader has it open. This is too
restrictive. Write access is denied even when the reader has
reached end-of-file. And tracking read access (which is much more
common than write access) causes havoc when remote hosts crash or
disconnect.
</P>
<P>
It is bizarre that the concept of multi-user contention for
modifying files has not been adequately addressed by either of the
large operating system development efforts. There is further irony
that both camps support contention detection and resolution only
through weak conventions of some their document editing programs.
</P>
<P>
<A NAME="IDX1616"></A>
The <EM>file-lock</EM> procedures implement a transaction method for file
<A NAME="IDX1617"></A>
replacement compatible with the methods used by the GNU <EM>emacs</EM>
<A NAME="IDX1618"></A>
text editor on Unix systems and the Microsoft <EM>Word</EM> editor.
<A NAME="IDX1619"></A>
<A NAME="IDX1620"></A>
</P>
<P>
<A NAME="IDX1621"></A>
Both protocols employ what I term a <EM>certificate</EM> containing the
<A NAME="IDX1622"></A>
user, hostname, time, and (on Unix) process-id.
Intent to replace <VAR>file</VAR> is indicated by adding to <VAR>file</VAR>'s
directory a certificate object whose name is derived from
<VAR>file</VAR>.
</P>
<P>
The Microsoft Word certificate is contained in a 162 byte file named
for the visited <VAR>file</VAR> with a `<SAMP>~$</SAMP>' prefix.
Emacs/Unix creates a symbolic link to a certificate named for the
visited <VAR>file</VAR> prefixed with `<SAMP>.#</SAMP>'.
Because Unix systems can import Microsoft file systems, these
routines maintain and check both Emacs and Word certificates.
</P>
<P>
<A NAME="IDX1623"></A>
</P>
<DL>
<DT><U>Function:</U> <B>file-lock-owner</B> <I>path</I>
<DD><P>
Returns the string `<SAMP><VAR>user</VAR>@<VAR>hostname</VAR></SAMP>' associated with
the lock owner of file <VAR>path</VAR> if locked; and #f otherwise.
</P>
</DL>
<P>
<A NAME="IDX1624"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>file-lock!</B> <I>path email</I>
<DD><P>
<A NAME="IDX1625"></A>
<DT><U>Procedure:</U> <B>file-lock!</B> <I>path</I>
<DD></P>
<P>
<VAR>path</VAR> must be a string naming the file to be locked. If supplied, <VAR>email</VAR>
must be a string formatted as `<SAMP><VAR>user</VAR>@<VAR>hostname</VAR></SAMP>'. If
absent, <VAR>email</VAR> defaults to the value returned by <CODE>user-email-address</CODE>.
</P>
<P>
If <VAR>path</VAR> is already locked, then <CODE>file-lock!</CODE> returns `<SAMP>#f</SAMP>'. If <VAR>path</VAR> is
unlocked, then <CODE>file-lock!</CODE> returns the certificate string associated with the
new lock for file <VAR>path</VAR>.
</P>
</DL>
<P>
<A NAME="IDX1626"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>file-unlock!</B> <I>path certificate</I>
<DD><P>
<VAR>path</VAR> must be a string naming the file to be unlocked. <VAR>certificate</VAR> must be the
string returned by <CODE>file-lock!</CODE> for <VAR>path</VAR>.
</P>
<P>
If <VAR>path</VAR> is locked with <VAR>certificate</VAR>, then <CODE>file-unlock!</CODE> removes the locks and returns
`<SAMP>#t</SAMP>'. Otherwise, <CODE>file-unlock!</CODE> leaves the file system unaltered and returns
`<SAMP>#f</SAMP>'.
</P>
</DL>
<A NAME="SEC273"></A>
<H4> File Transactions </H4>
<!--docid::SEC273::-->
<P>
<A NAME="IDX1627"></A>
</P>
<DL>
<DT><U>Function:</U> <B>emacs:backup-name</B> <I>path backup-style</I>
<DD><P>
<VAR>path</VAR> must be a string. <VAR>backup-style</VAR> must be a symbol. Depending on <VAR>backup-style</VAR>, <CODE>emacs:backup-name</CODE>
returns:
</P>
<DL COMPACT>
<DT>none
<DD>#f
<DT>simple
<DD>the string "<VAR>path</VAR>~"
<DT>numbered
<DD>the string "<VAR>path</VAR>.~<VAR>n</VAR>~", where <VAR>n</VAR> is one greater than the
highest number appearing in a filename matching "<VAR>path</VAR>.~*~". <VAR>n</VAR>
defauls to 1 when no filename matches.
<DT>existing
<DD>the string "<VAR>path</VAR>.~<VAR>n</VAR>~" if a numbered backup already exists in
this directory; otherwise. "<VAR>path</VAR>~"
<DT>orig
<DD>the string "<VAR>path</VAR>.orig"
<DT>bak
<DD>the string "<VAR>path</VAR>.bak"
</DL>
</DL>
<P>
<A NAME="IDX1628"></A>
</P>
<DL>
<DT><U>Function:</U> <B>transact-file-replacement</B> <I>proc path backup-style certificate</I>
<DD><P>
<A NAME="IDX1629"></A>
<DT><U>Function:</U> <B>transact-file-replacement</B> <I>proc path backup-style</I>
<DD></P>
<P>
<A NAME="IDX1630"></A>
<DT><U>Function:</U> <B>transact-file-replacement</B> <I>proc path</I>
<DD></P>
<P>
<VAR>path</VAR> must be a string naming an existing file. <VAR>backup-style</VAR> is one of the
symbols none, simple, numbered, existing, orig,
bak or #f; with meanings described above; or a string naming
the location of a backup file. <VAR>backup-style</VAR> defaults to #f. If supplied,
<VAR>certificate</VAR> is the certificate with which <VAR>path</VAR> is locked.
</P>
<P>
<VAR>proc</VAR> must be a procedure taking two string arguments:
<UL>
<LI>
<VAR>path</VAR>, the original filename (to be read); and
<LI>
a temporary file-name.
</UL>
<P>
If <VAR>path</VAR> is locked by other than <VAR>certificate</VAR>, or if <VAR>certificate</VAR> is supplied and <VAR>path</VAR> is not
locked, then <CODE>transact-file-replacement</CODE> returns #f. If <VAR>certificate</VAR> is not supplied, then, <CODE>transact-file-replacement</CODE> creates
temporary (Emacs and Word) locks for <VAR>path</VAR> during the transaction. The
lock status of <VAR>path</VAR> will be restored before <CODE>transact-file-replacement</CODE> returns.
</P>
<P>
<CODE>transact-file-replacement</CODE> calls <VAR>proc</VAR> with <VAR>path</VAR> (which should not be modified) and a temporary
file path to be written.
If <VAR>proc</VAR> returns any value other than #t, then the file named by <VAR>path</VAR>
is not altered and <CODE>transact-file-replacement</CODE> returns #f.
Otherwise, <CODE>emacs:backup-name</CODE> is called with <VAR>path</VAR> and <VAR>backup-style</VAR>. If it
returns a string, then <VAR>path</VAR> is renamed to it.
</P>
<P>
Finally, the temporary file is renamed <VAR>path</VAR>.
<CODE>transact-file-replacement</CODE> returns #t if <VAR>path</VAR> was successfully replaced; and #f otherwise.
</P>
</DL>
<A NAME="SEC274"></A>
<H4> Identification </H4>
<!--docid::SEC274::-->
<P>
<A NAME="IDX1631"></A>
</P>
<DL>
<DT><U>Function:</U> <B>user-email-address</B>
<DD><P>
<CODE>user-email-address</CODE> returns a string of the form `<SAMP>username@hostname</SAMP>'. If
this e-mail address cannot be obtained, #f is returned.
</P>
</DL>
<P>
<A NAME="CVS"></A>
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<H3> 7.6.3 CVS </H3>
<!--docid::SEC275::-->
<P>
<CODE>(require 'cvs)</CODE>
<A NAME="IDX1632"></A>
</P>
<P>
<A NAME="IDX1633"></A>
</P>
<DL>
<DT><U>Function:</U> <B>cvs-files</B> <I>directory/</I>
<DD>Returns a list of the local pathnames (with prefix <VAR>directory/</VAR>) of all
CVS controlled files in <VAR>directory/</VAR> and in <VAR>directory/</VAR>'s subdirectories.
</DL>
<P>
<A NAME="IDX1634"></A>
</P>
<DL>
<DT><U>Function:</U> <B>cvs-directories</B> <I>directory/</I>
<DD>Returns a list of all of <VAR>directory/</VAR> and all <VAR>directory/</VAR>'s CVS controlled
subdirectories.
</DL>
<P>
<A NAME="IDX1635"></A>
</P>
<DL>
<DT><U>Function:</U> <B>cvs-root</B> <I>path/</I>
<DD>Returns the (string) contents of <VAR>path/</VAR>CVS/Root;
or <CODE>(getenv "CVSROOT")</CODE> if Root doesn't exist.
</DL>
<P>
<A NAME="IDX1636"></A>
</P>
<DL>
<DT><U>Function:</U> <B>cvs-repository</B> <I>directory/</I>
<DD>Returns the (string) contents of <VAR>directory/</VAR>CVS/Root appended
with <VAR>directory/</VAR>CVS/Repository; or #f if <VAR>directory/</VAR>CVS/Repository
doesn't exist.
</DL>
<P>
<A NAME="IDX1637"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>cvs-set-root!</B> <I>new-root directory/</I>
<DD><P>
Writes <VAR>new-root</VAR> to file CVS/Root of <VAR>directory/</VAR> and all its subdirectories.
</P>
</DL>
<P>
<A NAME="IDX1638"></A>
</P>
<DL>
<DT><U>Function:</U> <B>cvs-vet</B> <I>directory/</I>
<DD><P>
Signals an error if CVS/Repository or CVS/Root files in <VAR>directory/</VAR> or any
subdirectory do not match.
</P>
</DL>
<P>
<A NAME="Extra-SLIB Packages"></A>
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<H2> 7.7 Extra-SLIB Packages </H2>
<!--docid::SEC276::-->
<P>
Several Scheme packages have been written using SLIB. There are several
reasons why a package might not be included in the SLIB distribution:
<UL>
<LI>
Because it requires special hardware or software which is not universal.
<LI>
Because it is large and of limited interest to most Scheme users.
<LI>
Because it has copying terms different enough from the other SLIB
packages that its inclusion would cause confusion.
<LI>
Because it is an application program, rather than a library module.
<LI>
Because I have been too busy to integrate it.
</UL>
<P>
Once an optional package is installed (and an entry added to
<CODE>*catalog*</CODE>, the <CODE>require</CODE> mechanism allows it to be called up
and used as easily as any other SLIB package. Some optional packages
(for which <CODE>*catalog*</CODE> already has entries) available from SLIB
sites are:
</P>
<P>
</P>
<DL COMPACT>
<DT>SLIB-PSD
<DD>is a portable debugger for Scheme (requires emacs editor).
<P>
<A HREF="http://swissnet.ai.mit.edu/ftpdir/scm/slib-psd1-3.tar.gz">
http://swissnet.ai.mit.edu/ftpdir/scm/slib-psd1-3.tar.gz
</A>
</P>
<P>
swissnet.ai.mit.edu:/pub/scm/slib-psd1-3.tar.gz
</P>
<P>
ftp.maths.tcd.ie:pub/bosullvn/jacal/slib-psd1-3.tar.gz
</P>
<P>
ftp.cs.indiana.edu:/pub/scheme-repository/utl/slib-psd1-3.tar.gz
</P>
<P>
With PSD, you can run a Scheme program in an Emacs buffer, set
breakpoints, single step evaluation and access and modify the program's
variables. It works by instrumenting the original source code, so it
should run with any R4RS compliant Scheme. It has been tested with SCM,
Elk 1.5, and the sci interpreter in the Scheme->C system, but should
work with other Schemes with a minimal amount of porting, if at
all. Includes documentation and user's manual. Written by Pertti
Kellom\"aki, pk @ cs.tut.fi. The Lisp Pointers article describing PSD
(Lisp Pointers VI(1):15-23, January-March 1993) is available as
<A HREF="http://www.cs.tut.fi/staff/pk/scheme/psd/article/article.html">
http://www.cs.tut.fi/staff/pk/scheme/psd/article/article.html
</A>
</P>
<P>
</P>
<DT>SCHELOG
<DD>is an embedding of Prolog in Scheme.<BR>
<A HREF="http://www.ccs.neu.edu/~dorai/schelog/schelog.html">
http://www.ccs.neu.edu/~dorai/schelog/schelog.html
</A>
<P>
</P>
<DT>JFILTER
<DD>is a Scheme program which converts text among the JIS, EUC, and
Shift-JIS Japanese character sets.<BR>
<A HREF="http://www.sci.toyama-u.ac.jp/~iwao/Scheme/Jfilter/index.html">
http://www.sci.toyama-u.ac.jp/~iwao/Scheme/Jfilter/index.html
</A>
</DL>
<P>
<A NAME="About SLIB"></A>
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