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-<TITLE>SLIB: Scheme Syntax Extension Packages</TITLE>
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-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
-</TR></TABLE>
-<H1> 3. Scheme Syntax Extension Packages </H1>
-<!--docid::SEC21::-->
-<P>
-
-<TABLE BORDER="0" CELLSPACING="0">
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC22">3.1 Defmacro</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Supported by all implementations</TD></TR>
-<TR><TH COLSPAN="3" ALIGN="left" VALIGN="TOP">
-</TH></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC24">3.2 R4RS Macros</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'macro</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC25">3.3 Macro by Example</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'macro-by-example</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC27">3.4 Macros That Work</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'macros-that-work</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC30">3.5 Syntactic Closures</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'syntactic-closures</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC36">3.6 Syntax-Case Macros</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'syntax-case</TD></TR>
-<TR><TH COLSPAN="3" ALIGN="left" VALIGN="TOP">
-</TH></TR>
-<TR><TH COLSPAN="3" ALIGN="left" VALIGN="TOP">Syntax extensions (macros) included with SLIB.
-</TH></TR>
-<TR><TH COLSPAN="3" ALIGN="left" VALIGN="TOP">
-</TH></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC39">3.7 Fluid-Let</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'fluid-let</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC40">3.8 Yasos</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">'yasos, 'oop, 'collect</TD></TR>
-</TABLE>
-<P>
-
-<A NAME="Defmacro"></A>
-<HR SIZE="6">
-<A NAME="SEC22"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt; </A>]</TD>
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-<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> 3.1 Defmacro </H2>
-<!--docid::SEC22::-->
-<P>
-
-Defmacros are supported by all implementations.
-</P>
-<P>
-
-<A NAME="IDX107"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>gentemp</B>
-<DD>Returns a new (interned) symbol each time it is called. The symbol
-names are implementation-dependent
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(gentemp) => scm:G0
-(gentemp) => scm:G1
-</pre></td></tr></table></DL>
-<P>
-
-<A NAME="IDX108"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>defmacro:eval</B> <I>e</I>
-<DD>Returns the <CODE>slib:eval</CODE> of expanding all defmacros in scheme
-expression <VAR>e</VAR>.
-</DL>
-<P>
-
-<A NAME="IDX109"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>defmacro:load</B> <I>filename</I>
-<DD><VAR>filename</VAR> should be a string. If filename names an existing file,
-the <CODE>defmacro:load</CODE> procedure reads Scheme source code expressions
-and definitions from the file and evaluates them sequentially. These
-source code expressions and definitions may contain defmacro
-definitions. The <CODE>macro:load</CODE> procedure does not affect the values
-returned by <CODE>current-input-port</CODE> and
-<CODE>current-output-port</CODE>.
-</DL>
-<P>
-
-<A NAME="IDX110"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>defmacro?</B> <I>sym</I>
-<DD>Returns <CODE>#t</CODE> if <VAR>sym</VAR> has been defined by <CODE>defmacro</CODE>,
-<CODE>#f</CODE> otherwise.
-</DL>
-<P>
-
-<A NAME="IDX111"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macroexpand-1</B> <I>form</I>
-<DD><A NAME="IDX112"></A>
-<DT><U>Function:</U> <B>macroexpand</B> <I>form</I>
-<DD>If <VAR>form</VAR> is a macro call, <CODE>macroexpand-1</CODE> will expand the
-macro call once and return it. A <VAR>form</VAR> is considered to be a macro
-call only if it is a cons whose <CODE>car</CODE> is a symbol for which a
-<CODE>defmacro</CODE> has been defined.
-<P>
-
-<CODE>macroexpand</CODE> is similar to <CODE>macroexpand-1</CODE>, but repeatedly
-expands <VAR>form</VAR> until it is no longer a macro call.
-</P>
-</DL>
-<P>
-
-<A NAME="IDX113"></A>
-</P>
-<DL>
-<DT><U>Macro:</U> <B>defmacro</B> <I>name lambda-list form <small>...</small></I>
-<DD>When encountered by <CODE>defmacro:eval</CODE>, <CODE>defmacro:macroexpand*</CODE>,
-or <CODE>defmacro:load</CODE> defines a new macro which will henceforth be
-expanded when encountered by <CODE>defmacro:eval</CODE>,
-<CODE>defmacro:macroexpand*</CODE>, or <CODE>defmacro:load</CODE>.
-</DL>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC23"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC22"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC24"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.1.1 Defmacroexpand </H3>
-<!--docid::SEC23::-->
-<CODE>(require 'defmacroexpand)</CODE>
-<A NAME="IDX114"></A>
-<P>
-
-<A NAME="IDX115"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>defmacro:expand*</B> <I>e</I>
-<DD>Returns the result of expanding all defmacros in scheme expression
-<VAR>e</VAR>.
-</DL>
-<P>
-
-<A NAME="R4RS Macros"></A>
-<HR SIZE="6">
-<A NAME="SEC24"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC23"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC25"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.2 R4RS Macros </H2>
-<!--docid::SEC24::-->
-<P>
-
-<CODE>(require 'macro)</CODE> is the appropriate call if you want R4RS
-<A NAME="IDX116"></A>
-high-level macros but don't care about the low level implementation. If
-an SLIB R4RS macro implementation is already loaded it will be used.
-Otherwise, one of the R4RS macros implemetations is loaded.
-</P>
-<P>
-
-The SLIB R4RS macro implementations support the following uniform
-interface:
-</P>
-<P>
-
-<A NAME="IDX117"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:expand</B> <I>sexpression</I>
-<DD>Takes an R4RS expression, macro-expands it, and returns the result of
-the macro expansion.
-</DL>
-<P>
-
-<A NAME="IDX118"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:eval</B> <I>sexpression</I>
-<DD>Takes an R4RS expression, macro-expands it, evals the result of the
-macro expansion, and returns the result of the evaluation.
-</DL>
-<P>
-
-<A NAME="IDX119"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>macro:load</B> <I>filename</I>
-<DD><VAR>filename</VAR> should be a string. If filename names an existing file,
-the <CODE>macro:load</CODE> procedure reads Scheme source code expressions and
-definitions from the file and evaluates them sequentially. These source
-code expressions and definitions may contain macro definitions. The
-<CODE>macro:load</CODE> procedure does not affect the values returned by
-<CODE>current-input-port</CODE> and <CODE>current-output-port</CODE>.
-</DL>
-<P>
-
-<A NAME="Macro by Example"></A>
-<HR SIZE="6">
-<A NAME="SEC25"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC24"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC26"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.3 Macro by Example </H2>
-<!--docid::SEC25::-->
-<P>
-
-<CODE>(require 'macro-by-example)</CODE>
-<A NAME="IDX120"></A>
-</P>
-<P>
-
-A vanilla implementation of <CITE>Macro by Example</CITE> (Eugene Kohlbecker,
-R4RS) by Dorai Sitaram, (dorai @ cs.rice.edu) using <CODE>defmacro</CODE>.
-</P>
-<P>
-
-<UL>
-
-<LI>
-generating hygienic global <CODE>define-syntax</CODE> Macro-by-Example macros
-<STRONG>cheaply</STRONG>.
-<P>
-
-</P>
-<LI>
-can define macros which use <CODE>...</CODE>.
-<P>
-
-</P>
-<LI>
-needn't worry about a lexical variable in a macro definition
-clashing with a variable from the macro use context
-<P>
-
-</P>
-<LI>
-don't suffer the overhead of redefining the repl if <CODE>defmacro</CODE>
-natively supported (most implementations)
-<P>
-
-</UL>
-<HR SIZE="6">
-<A NAME="SEC26"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC25"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC27"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.3.1 Caveat </H3>
-<!--docid::SEC26::-->
-These macros are not referentially transparent (see section `Macros' in <CITE>Revised(4) Scheme</CITE>). Lexically scoped macros (i.e., <CODE>let-syntax</CODE>
-and <CODE>letrec-syntax</CODE>) are not supported. In any case, the problem
-of referential transparency gains poignancy only when <CODE>let-syntax</CODE>
-and <CODE>letrec-syntax</CODE> are used. So you will not be courting
-large-scale disaster unless you're using system-function names as local
-variables with unintuitive bindings that the macro can't use. However,
-if you must have the full <CITE>r4rs</CITE> macro functionality, look to the
-more featureful (but also more expensive) versions of syntax-rules
-available in slib <A HREF="slib_3.html#SEC27">3.4 Macros That Work</A>, <A HREF="slib_3.html#SEC30">3.5 Syntactic Closures</A>, and
-<A HREF="slib_3.html#SEC36">3.6 Syntax-Case Macros</A>.
-<P>
-
-<A NAME="IDX121"></A>
-</P>
-<DL>
-<DT><U>Macro:</U> <B>define-syntax</B> <I>keyword transformer-spec</I>
-<DD>The <VAR>keyword</VAR> is an identifier, and the <VAR>transformer-spec</VAR>
-should be an instance of <CODE>syntax-rules</CODE>.
-<P>
-
-The top-level syntactic environment is extended by binding the
-<VAR>keyword</VAR> to the specified transformer.
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax let*
- (syntax-rules ()
- ((let* () body1 body2 ...)
- (let () body1 body2 ...))
- ((let* ((name1 val1) (name2 val2) ...)
- body1 body2 ...)
- (let ((name1 val1))
- (let* (( name2 val2) ...)
- body1 body2 ...)))))
-</pre></td></tr></table></DL>
-<P>
-
-<A NAME="IDX122"></A>
-</P>
-<DL>
-<DT><U>Macro:</U> <B>syntax-rules</B> <I>literals syntax-rule <small>...</small></I>
-<DD><VAR>literals</VAR> is a list of identifiers, and each <VAR>syntax-rule</VAR>
-should be of the form
-<P>
-
-<CODE>(<VAR>pattern</VAR> <VAR>template</VAR>)</CODE>
-</P>
-<P>
-
-where the <VAR>pattern</VAR> and <VAR>template</VAR> are as in the grammar above.
-</P>
-<P>
-
-An instance of <CODE>syntax-rules</CODE> produces a new macro transformer by
-specifying a sequence of hygienic rewrite rules. A use of a macro whose
-keyword is associated with a transformer specified by
-<CODE>syntax-rules</CODE> is matched against the patterns contained in the
-<VAR>syntax-rule</VAR>s, beginning with the leftmost <VAR>syntax-rule</VAR>.
-When a match is found, the macro use is trancribed hygienically
-according to the template.
-</P>
-<P>
-
-Each pattern begins with the keyword for the macro. This keyword is not
-involved in the matching and is not considered a pattern variable or
-literal identifier.
-</P>
-</DL>
-<P>
-
-<A NAME="Macros That Work"></A>
-<HR SIZE="6">
-<A NAME="SEC27"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC26"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC28"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.4 Macros That Work </H2>
-<!--docid::SEC27::-->
-<P>
-
-<CODE>(require 'macros-that-work)</CODE>
-<A NAME="IDX123"></A>
-</P>
-<P>
-
-<CITE>Macros That Work</CITE> differs from the other R4RS macro
-implementations in that it does not expand derived expression types to
-primitive expression types.
-</P>
-<P>
-
-<A NAME="IDX124"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:expand</B> <I>expression</I>
-<DD><A NAME="IDX125"></A>
-<DT><U>Function:</U> <B>macwork:expand</B> <I>expression</I>
-<DD>Takes an R4RS expression, macro-expands it, and returns the result of
-the macro expansion.
-</DL>
-<P>
-
-<A NAME="IDX126"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:eval</B> <I>expression</I>
-<DD><A NAME="IDX127"></A>
-<DT><U>Function:</U> <B>macwork:eval</B> <I>expression</I>
-<DD><CODE>macro:eval</CODE> returns the value of <VAR>expression</VAR> in the current
-top level environment. <VAR>expression</VAR> can contain macro definitions.
-Side effects of <VAR>expression</VAR> will affect the top level
-environment.
-</DL>
-<P>
-
-<A NAME="IDX128"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>macro:load</B> <I>filename</I>
-<DD><A NAME="IDX129"></A>
-<DT><U>Procedure:</U> <B>macwork:load</B> <I>filename</I>
-<DD><VAR>filename</VAR> should be a string. If filename names an existing file,
-the <CODE>macro:load</CODE> procedure reads Scheme source code expressions and
-definitions from the file and evaluates them sequentially. These source
-code expressions and definitions may contain macro definitions. The
-<CODE>macro:load</CODE> procedure does not affect the values returned by
-<CODE>current-input-port</CODE> and <CODE>current-output-port</CODE>.
-</DL>
-<P>
-
-References:
-</P>
-<P>
-
-The <CITE>Revised^4 Report on the Algorithmic Language Scheme</CITE> Clinger
-and Rees [editors]. To appear in LISP Pointers. Also available as a
-technical report from the University of Oregon, MIT AI Lab, and
-Cornell.
-</P>
-<P>
-
-<center>
- Macros That Work. Clinger and Rees. POPL '91.
-</center>
-</P>
-<P>
-
-The supported syntax differs from the R4RS in that vectors are allowed
-as patterns and as templates and are not allowed as pattern or template
-data.
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>transformer spec ==> (syntax-rules literals rules)
-
-rules ==> ()
- | (rule . rules)
-
-rule ==> (pattern template)
-
-pattern ==> pattern_var ; a symbol not in literals
- | symbol ; a symbol in literals
- | ()
- | (pattern . pattern)
- | (ellipsis_pattern)
- | #(pattern*) ; extends R4RS
- | #(pattern* ellipsis_pattern) ; extends R4RS
- | pattern_datum
-
-template ==> pattern_var
- | symbol
- | ()
- | (template2 . template2)
- | #(template*) ; extends R4RS
- | pattern_datum
-
-template2 ==> template
- | ellipsis_template
-
-pattern_datum ==> string ; no vector
- | character
- | boolean
- | number
-
-ellipsis_pattern ==> pattern ...
-
-ellipsis_template ==> template ...
-
-pattern_var ==> symbol ; not in literals
-
-literals ==> ()
- | (symbol . literals)
-</pre></td></tr></table><P>
-
-<HR SIZE="6">
-<A NAME="SEC28"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_toc.html#SEC_Contents">Contents</A>]</TD>
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-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
-</TR></TABLE>
-<H3> 3.4.1 Definitions </H3>
-<!--docid::SEC28::-->
-<P>
-
-</P>
-<DL COMPACT>
-
-<DT>Scope of an ellipsis
-<DD>Within a pattern or template, the scope of an ellipsis (<CODE>...</CODE>) is
-the pattern or template that appears to its left.
-<P>
-
-</P>
-<DT>Rank of a pattern variable
-<DD>The rank of a pattern variable is the number of ellipses within whose
-scope it appears in the pattern.
-<P>
-
-</P>
-<DT>Rank of a subtemplate
-<DD>The rank of a subtemplate is the number of ellipses within whose scope
-it appears in the template.
-<P>
-
-</P>
-<DT>Template rank of an occurrence of a pattern variable
-<DD>The template rank of an occurrence of a pattern variable within a
-template is the rank of that occurrence, viewed as a subtemplate.
-<P>
-
-</P>
-<DT>Variables bound by a pattern
-<DD>The variables bound by a pattern are the pattern variables that appear
-within it.
-<P>
-
-</P>
-<DT>Referenced variables of a subtemplate
-<DD>The referenced variables of a subtemplate are the pattern variables that
-appear within it.
-<P>
-
-</P>
-<DT>Variables opened by an ellipsis template
-<DD>The variables opened by an ellipsis template are the referenced pattern
-variables whose rank is greater than the rank of the ellipsis template.
-<P>
-
-</DL>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC29"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC28"> &lt; </A>]</TD>
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-<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> 3.4.2 Restrictions </H3>
-<!--docid::SEC29::-->
-<P>
-
-No pattern variable appears more than once within a pattern.
-</P>
-<P>
-
-For every occurrence of a pattern variable within a template, the
-template rank of the occurrence must be greater than or equal to the
-pattern variable's rank.
-</P>
-<P>
-
-Every ellipsis template must open at least one variable.
-</P>
-<P>
-
-For every ellipsis template, the variables opened by an ellipsis
-template must all be bound to sequences of the same length.
-</P>
-<P>
-
-The compiled form of a <VAR>rule</VAR> is
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>rule ==> (pattern template inserted)
-
-pattern ==> pattern_var
- | symbol
- | ()
- | (pattern . pattern)
- | ellipsis_pattern
- | #(pattern)
- | pattern_datum
-
-template ==> pattern_var
- | symbol
- | ()
- | (template2 . template2)
- | #(pattern)
- | pattern_datum
-
-template2 ==> template
- | ellipsis_template
-
-pattern_datum ==> string
- | character
- | boolean
- | number
-
-pattern_var ==> #(V symbol rank)
-
-ellipsis_pattern ==> #(E pattern pattern_vars)
-
-ellipsis_template ==> #(E template pattern_vars)
-
-inserted ==> ()
- | (symbol . inserted)
-
-pattern_vars ==> ()
- | (pattern_var . pattern_vars)
-
-rank ==> exact non-negative integer
-</pre></td></tr></table><P>
-
-where V and E are unforgeable values.
-</P>
-<P>
-
-The pattern variables associated with an ellipsis pattern are the
-variables bound by the pattern, and the pattern variables associated
-with an ellipsis template are the variables opened by the ellipsis
-template.
-</P>
-<P>
-
-If the template contains a big chunk that contains no pattern variables
-or inserted identifiers, then the big chunk will be copied
-unnecessarily. That shouldn't matter very often.
-</P>
-<P>
-
-<A NAME="Syntactic Closures"></A>
-<HR SIZE="6">
-<A NAME="SEC30"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC29"> &lt; </A>]</TD>
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-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
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-<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> 3.5 Syntactic Closures </H2>
-<!--docid::SEC30::-->
-<P>
-
-<CODE>(require 'syntactic-closures)</CODE>
-<A NAME="IDX130"></A>
-</P>
-<P>
-
-<A NAME="IDX131"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:expand</B> <I>expression</I>
-<DD><A NAME="IDX132"></A>
-<DT><U>Function:</U> <B>synclo:expand</B> <I>expression</I>
-<DD>Returns scheme code with the macros and derived expression types of
-<VAR>expression</VAR> expanded to primitive expression types.
-</DL>
-<P>
-
-<A NAME="IDX133"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:eval</B> <I>expression</I>
-<DD><A NAME="IDX134"></A>
-<DT><U>Function:</U> <B>synclo:eval</B> <I>expression</I>
-<DD><CODE>macro:eval</CODE> returns the value of <VAR>expression</VAR> in the current
-top level environment. <VAR>expression</VAR> can contain macro definitions.
-Side effects of <VAR>expression</VAR> will affect the top level
-environment.
-</DL>
-<P>
-
-<A NAME="IDX135"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>macro:load</B> <I>filename</I>
-<DD><A NAME="IDX136"></A>
-<DT><U>Procedure:</U> <B>synclo:load</B> <I>filename</I>
-<DD><VAR>filename</VAR> should be a string. If filename names an existing file,
-the <CODE>macro:load</CODE> procedure reads Scheme source code expressions and
-definitions from the file and evaluates them sequentially. These
-source code expressions and definitions may contain macro definitions.
-The <CODE>macro:load</CODE> procedure does not affect the values returned by
-<CODE>current-input-port</CODE> and <CODE>current-output-port</CODE>.
-</DL>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC31"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC30"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC32"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.5.1 Syntactic Closure Macro Facility </H3>
-<!--docid::SEC31::-->
-<P>
-
-<center>
- A Syntactic Closures Macro Facility
-</center>
-<center>
- by Chris Hanson
-</center>
-<center>
- 9 November 1991
-</center>
-</P>
-<P>
-
-This document describes <EM>syntactic closures</EM>, a low-level macro
-facility for the Scheme programming language. The facility is an
-alternative to the low-level macro facility described in the
-<CITE>Revised^4 Report on Scheme.</CITE> This document is an addendum to that
-report.
-</P>
-<P>
-
-The syntactic closures facility extends the BNF rule for
-<VAR>transformer spec</VAR> to allow a new keyword that introduces a
-low-level macro transformer:
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre><VAR>transformer spec</VAR> := (transformer <VAR>expression</VAR>)
-</pre></td></tr></table><P>
-
-Additionally, the following procedures are added:
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>make-syntactic-closure
-capture-syntactic-environment
-identifier?
-identifier=?
-</pre></td></tr></table><P>
-
-The description of the facility is divided into three parts. The first
-part defines basic terminology. The second part describes how macro
-transformers are defined. The third part describes the use of
-<EM>identifiers</EM>, which extend the syntactic closure mechanism to be
-compatible with <CODE>syntax-rules</CODE>.
-</P>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC32"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC31"> &lt; </A>]</TD>
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-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
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-<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> 3.5.1.1 Terminology </H4>
-<!--docid::SEC32::-->
-<P>
-
-This section defines the concepts and data types used by the syntactic
-closures facility.
-</P>
-<P>
-
-<UL>
-
-<LI><EM>Forms</EM> are the syntactic entities out of which programs are
-recursively constructed. A form is any expression, any definition, any
-syntactic keyword, or any syntactic closure. The variable name that
-appears in a <CODE>set!</CODE> special form is also a form. Examples of
-forms:
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>17
-#t
-car
-(+ x 4)
-(lambda (x) x)
-(define pi 3.14159)
-if
-define
-</pre></td></tr></table><P>
-
-</P>
-<LI>An <EM>alias</EM> is an alternate name for a given symbol. It can
-appear anywhere in a form that the symbol could be used, and when quoted
-it is replaced by the symbol; however, it does not satisfy the predicate
-<CODE>symbol?</CODE>. Macro transformers rarely distinguish symbols from
-aliases, referring to both as identifiers.
-<P>
-
-</P>
-<LI>A <EM>syntactic</EM> environment maps identifiers to their
-meanings. More precisely, it determines whether an identifier is a
-syntactic keyword or a variable. If it is a keyword, the meaning is an
-interpretation for the form in which that keyword appears. If it is a
-variable, the meaning identifies which binding of that variable is
-referenced. In short, syntactic environments contain all of the
-contextual information necessary for interpreting the meaning of a
-particular form.
-<P>
-
-</P>
-<LI>A <EM>syntactic closure</EM> consists of a form, a syntactic
-environment, and a list of identifiers. All identifiers in the form
-take their meaning from the syntactic environment, except those in the
-given list. The identifiers in the list are to have their meanings
-determined later. A syntactic closure may be used in any context in
-which its form could have been used. Since a syntactic closure is also
-a form, it may not be used in contexts where a form would be illegal.
-For example, a form may not appear as a clause in the cond special form.
-A syntactic closure appearing in a quoted structure is replaced by its
-form.
-<P>
-
-</UL>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC33"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC32"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC34"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.5.1.2 Transformer Definition </H4>
-<!--docid::SEC33::-->
-<P>
-
-This section describes the <CODE>transformer</CODE> special form and the
-procedures <CODE>make-syntactic-closure</CODE> and
-<CODE>capture-syntactic-environment</CODE>.
-</P>
-<P>
-
-<A NAME="IDX137"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>transformer</B> <I>expression</I>
-<DD><P>
-
-Syntax: It is an error if this syntax occurs except as a
-<VAR>transformer spec</VAR>.
-</P>
-<P>
-
-Semantics: The <VAR>expression</VAR> is evaluated in the standard transformer
-environment to yield a macro transformer as described below. This macro
-transformer is bound to a macro keyword by the special form in which the
-<CODE>transformer</CODE> expression appears (for example,
-<CODE>let-syntax</CODE>).
-</P>
-<P>
-
-A <EM>macro transformer</EM> is a procedure that takes two arguments, a
-form and a syntactic environment, and returns a new form. The first
-argument, the <EM>input form</EM>, is the form in which the macro keyword
-occurred. The second argument, the <EM>usage environment</EM>, is the
-syntactic environment in which the input form occurred. The result of
-the transformer, the <EM>output form</EM>, is automatically closed in the
-<EM>transformer environment</EM>, which is the syntactic environment in
-which the <CODE>transformer</CODE> expression occurred.
-</P>
-<P>
-
-For example, here is a definition of a push macro using
-<CODE>syntax-rules</CODE>:
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax push
- (syntax-rules ()
- ((push item list)
- (set! list (cons item list)))))
-</pre></td></tr></table><P>
-
-Here is an equivalent definition using <CODE>transformer</CODE>:
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax push
- (transformer
- (lambda (exp env)
- (let ((item
- (make-syntactic-closure env '() (cadr exp)))
- (list
- (make-syntactic-closure env '() (caddr exp))))
- `(set! ,list (cons ,item ,list))))))
-</pre></td></tr></table><P>
-
-In this example, the identifiers <CODE>set!</CODE> and <CODE>cons</CODE> are closed
-in the transformer environment, and thus will not be affected by the
-meanings of those identifiers in the usage environment
-<CODE>env</CODE>.
-</P>
-<P>
-
-Some macros may be non-hygienic by design. For example, the following
-defines a loop macro that implicitly binds <CODE>exit</CODE> to an escape
-procedure. The binding of <CODE>exit</CODE> is intended to capture free
-references to <CODE>exit</CODE> in the body of the loop, so <CODE>exit</CODE> must
-be left free when the body is closed:
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax loop
- (transformer
- (lambda (exp env)
- (let ((body (cdr exp)))
- `(call-with-current-continuation
- (lambda (exit)
- (let f ()
- ,@(map (lambda (exp)
- (make-syntactic-closure env '(exit)
- exp))
- body)
- (f))))))))
-</pre></td></tr></table><P>
-
-To assign meanings to the identifiers in a form, use
-<CODE>make-syntactic-closure</CODE> to close the form in a syntactic
-environment.
-</P>
-</DL>
-<P>
-
-<A NAME="IDX138"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>make-syntactic-closure</B> <I>environment free-names form</I>
-<DD><P>
-
-<VAR>environment</VAR> must be a syntactic environment, <VAR>free-names</VAR> must
-be a list of identifiers, and <VAR>form</VAR> must be a form.
-<CODE>make-syntactic-closure</CODE> constructs and returns a syntactic closure
-of <VAR>form</VAR> in <VAR>environment</VAR>, which can be used anywhere that
-<VAR>form</VAR> could have been used. All the identifiers used in
-<VAR>form</VAR>, except those explicitly excepted by <VAR>free-names</VAR>, obtain
-their meanings from <VAR>environment</VAR>.
-</P>
-<P>
-
-Here is an example where <VAR>free-names</VAR> is something other than the
-empty list. It is instructive to compare the use of <VAR>free-names</VAR> in
-this example with its use in the <CODE>loop</CODE> example above: the examples
-are similar except for the source of the identifier being left
-free.
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax let1
- (transformer
- (lambda (exp env)
- (let ((id (cadr exp))
- (init (caddr exp))
- (exp (cadddr exp)))
- `((lambda (,id)
- ,(make-syntactic-closure env (list id) exp))
- ,(make-syntactic-closure env '() init))))))
-</pre></td></tr></table><P>
-
-<CODE>let1</CODE> is a simplified version of <CODE>let</CODE> that only binds a
-single identifier, and whose body consists of a single expression. When
-the body expression is syntactically closed in its original syntactic
-environment, the identifier that is to be bound by <CODE>let1</CODE> must be
-left free, so that it can be properly captured by the <CODE>lambda</CODE> in
-the output form.
-</P>
-<P>
-
-To obtain a syntactic environment other than the usage environment, use
-<CODE>capture-syntactic-environment</CODE>.
-</P>
-</DL>
-<P>
-
-<A NAME="IDX139"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>capture-syntactic-environment</B> <I>procedure</I>
-<DD><P>
-
-<CODE>capture-syntactic-environment</CODE> returns a form that will, when
-transformed, call <VAR>procedure</VAR> on the current syntactic environment.
-<VAR>procedure</VAR> should compute and return a new form to be transformed,
-in that same syntactic environment, in place of the form.
-</P>
-<P>
-
-An example will make this clear. Suppose we wanted to define a simple
-<CODE>loop-until</CODE> keyword equivalent to
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax loop-until
- (syntax-rules ()
- ((loop-until id init test return step)
- (letrec ((loop
- (lambda (id)
- (if test return (loop step)))))
- (loop init)))))
-</pre></td></tr></table><P>
-
-The following attempt at defining <CODE>loop-until</CODE> has a subtle bug:
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax loop-until
- (transformer
- (lambda (exp env)
- (let ((id (cadr exp))
- (init (caddr exp))
- (test (cadddr exp))
- (return (cadddr (cdr exp)))
- (step (cadddr (cddr exp)))
- (close
- (lambda (exp free)
- (make-syntactic-closure env free exp))))
- `(letrec ((loop
- (lambda (,id)
- (if ,(close test (list id))
- ,(close return (list id))
- (loop ,(close step (list id)))))))
- (loop ,(close init '())))))))
-</pre></td></tr></table><P>
-
-This definition appears to take all of the proper precautions to prevent
-unintended captures. It carefully closes the subexpressions in their
-original syntactic environment and it leaves the <CODE>id</CODE> identifier
-free in the <CODE>test</CODE>, <CODE>return</CODE>, and <CODE>step</CODE> expressions, so
-that it will be captured by the binding introduced by the <CODE>lambda</CODE>
-expression. Unfortunately it uses the identifiers <CODE>if</CODE> and
-<CODE>loop</CODE> within that <CODE>lambda</CODE> expression, so if the user of
-<CODE>loop-until</CODE> just happens to use, say, <CODE>if</CODE> for the
-identifier, it will be inadvertently captured.
-</P>
-<P>
-
-The syntactic environment that <CODE>if</CODE> and <CODE>loop</CODE> want to be
-exposed to is the one just outside the <CODE>lambda</CODE> expression: before
-the user's identifier is added to the syntactic environment, but after
-the identifier loop has been added.
-<CODE>capture-syntactic-environment</CODE> captures exactly that environment
-as follows:
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define-syntax loop-until
- (transformer
- (lambda (exp env)
- (let ((id (cadr exp))
- (init (caddr exp))
- (test (cadddr exp))
- (return (cadddr (cdr exp)))
- (step (cadddr (cddr exp)))
- (close
- (lambda (exp free)
- (make-syntactic-closure env free exp))))
- `(letrec ((loop
- ,(capture-syntactic-environment
- (lambda (env)
- `(lambda (,id)
- (,(make-syntactic-closure env '() `if)
- ,(close test (list id))
- ,(close return (list id))
- (,(make-syntactic-closure env '()
- `loop)
- ,(close step (list id)))))))))
- (loop ,(close init '())))))))
-</pre></td></tr></table><P>
-
-In this case, having captured the desired syntactic environment, it is
-convenient to construct syntactic closures of the identifiers <CODE>if</CODE>
-and the <CODE>loop</CODE> and use them in the body of the
-<CODE>lambda</CODE>.
-</P>
-<P>
-
-A common use of <CODE>capture-syntactic-environment</CODE> is to get the
-transformer environment of a macro transformer:
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(transformer
- (lambda (exp env)
- (capture-syntactic-environment
- (lambda (transformer-env)
- ...))))
-</pre></td></tr></table></DL>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC34"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC33"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC35"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.5.1.3 Identifiers </H4>
-<!--docid::SEC34::-->
-<P>
-
-This section describes the procedures that create and manipulate
-identifiers. Previous syntactic closure proposals did not have an
-identifier data type -- they just used symbols. The identifier data
-type extends the syntactic closures facility to be compatible with the
-high-level <CODE>syntax-rules</CODE> facility.
-</P>
-<P>
-
-As discussed earlier, an identifier is either a symbol or an
-<EM>alias</EM>. An alias is implemented as a syntactic closure whose
-<EM>form</EM> is an identifier:
-</P>
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(make-syntactic-closure env '() 'a)
- => an <EM>alias</EM>
-</pre></td></tr></table><P>
-
-Aliases are implemented as syntactic closures because they behave just
-like syntactic closures most of the time. The difference is that an
-alias may be bound to a new value (for example by <CODE>lambda</CODE> or
-<CODE>let-syntax</CODE>); other syntactic closures may not be used this way.
-If an alias is bound, then within the scope of that binding it is looked
-up in the syntactic environment just like any other identifier.
-</P>
-<P>
-
-Aliases are used in the implementation of the high-level facility
-<CODE>syntax-rules</CODE>. A macro transformer created by <CODE>syntax-rules</CODE>
-uses a template to generate its output form, substituting subforms of
-the input form into the template. In a syntactic closures
-implementation, all of the symbols in the template are replaced by
-aliases closed in the transformer environment, while the output form
-itself is closed in the usage environment. This guarantees that the
-macro transformation is hygienic, without requiring the transformer to
-know the syntactic roles of the substituted input subforms.
-</P>
-<P>
-
-<A NAME="IDX140"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>identifier?</B> <I>object</I>
-<DD>Returns <CODE>#t</CODE> if <VAR>object</VAR> is an identifier, otherwise returns
-<CODE>#f</CODE>. Examples:
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(identifier? 'a)
- => #t
-(identifier? (make-syntactic-closure env '() 'a))
- => #t
-(identifier? &quot;a&quot;)
- => #f
-(identifier? #\a)
- => #f
-(identifier? 97)
- => #f
-(identifier? #f)
- => #f
-(identifier? '(a))
- => #f
-(identifier? '#(a))
- => #f
-</pre></td></tr></table><P>
-
-The predicate <CODE>eq?</CODE> is used to determine if two identifers are
-&quot;the same&quot;. Thus <CODE>eq?</CODE> can be used to compare identifiers
-exactly as it would be used to compare symbols. Often, though, it is
-useful to know whether two identifiers &quot;mean the same thing&quot;. For
-example, the <CODE>cond</CODE> macro uses the symbol <CODE>else</CODE> to identify
-the final clause in the conditional. A macro transformer for
-<CODE>cond</CODE> cannot just look for the symbol <CODE>else</CODE>, because the
-<CODE>cond</CODE> form might be the output of another macro transformer that
-replaced the symbol <CODE>else</CODE> with an alias. Instead the transformer
-must look for an identifier that &quot;means the same thing&quot; in the usage
-environment as the symbol <CODE>else</CODE> means in the transformer
-environment.
-</P>
-</DL>
-<P>
-
-<A NAME="IDX141"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>identifier=?</B> <I>environment1 identifier1 environment2 identifier2</I>
-<DD><VAR>environment1</VAR> and <VAR>environment2</VAR> must be syntactic
-environments, and <VAR>identifier1</VAR> and <VAR>identifier2</VAR> must be
-identifiers. <CODE>identifier=?</CODE> returns <CODE>#t</CODE> if the meaning of
-<VAR>identifier1</VAR> in <VAR>environment1</VAR> is the same as that of
-<VAR>identifier2</VAR> in <VAR>environment2</VAR>, otherwise it returns <CODE>#f</CODE>.
-Examples:
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(let-syntax
- ((foo
- (transformer
- (lambda (form env)
- (capture-syntactic-environment
- (lambda (transformer-env)
- (identifier=? transformer-env 'x env 'x)))))))
- (list (foo)
- (let ((x 3))
- (foo))))
- => (#t #f)
-</pre></td></tr></table><P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(let-syntax ((bar foo))
- (let-syntax
- ((foo
- (transformer
- (lambda (form env)
- (capture-syntactic-environment
- (lambda (transformer-env)
- (identifier=? transformer-env 'foo
- env (cadr form))))))))
- (list (foo foo)
- (foobar))))
- => (#f #t)
-</pre></td></tr></table></DL>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC35"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC34"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC36"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.5.1.4 Acknowledgements </H4>
-<!--docid::SEC35::-->
-<P>
-
-The syntactic closures facility was invented by Alan Bawden and Jonathan
-Rees. The use of aliases to implement <CODE>syntax-rules</CODE> was invented
-by Alan Bawden (who prefers to call them <EM>synthetic names</EM>). Much
-of this proposal is derived from an earlier proposal by Alan
-Bawden.
-</P>
-<P>
-
-<A NAME="Syntax-Case Macros"></A>
-<HR SIZE="6">
-<A NAME="SEC36"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC35"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC37"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.6 Syntax-Case Macros </H2>
-<!--docid::SEC36::-->
-<P>
-
-<CODE>(require 'syntax-case)</CODE>
-<A NAME="IDX142"></A>
-</P>
-<P>
-
-<A NAME="IDX143"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:expand</B> <I>expression</I>
-<DD><A NAME="IDX144"></A>
-<DT><U>Function:</U> <B>syncase:expand</B> <I>expression</I>
-<DD>Returns scheme code with the macros and derived expression types of
-<VAR>expression</VAR> expanded to primitive expression types.
-</DL>
-<P>
-
-<A NAME="IDX145"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>macro:eval</B> <I>expression</I>
-<DD><A NAME="IDX146"></A>
-<DT><U>Function:</U> <B>syncase:eval</B> <I>expression</I>
-<DD><CODE>macro:eval</CODE> returns the value of <VAR>expression</VAR> in the current
-top level environment. <VAR>expression</VAR> can contain macro definitions.
-Side effects of <VAR>expression</VAR> will affect the top level
-environment.
-</DL>
-<P>
-
-<A NAME="IDX147"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>macro:load</B> <I>filename</I>
-<DD><A NAME="IDX148"></A>
-<DT><U>Procedure:</U> <B>syncase:load</B> <I>filename</I>
-<DD><VAR>filename</VAR> should be a string. If filename names an existing file,
-the <CODE>macro:load</CODE> procedure reads Scheme source code expressions and
-definitions from the file and evaluates them sequentially. These
-source code expressions and definitions may contain macro definitions.
-The <CODE>macro:load</CODE> procedure does not affect the values returned by
-<CODE>current-input-port</CODE> and <CODE>current-output-port</CODE>.
-</DL>
-<P>
-
-This is version 2.1 of <CODE>syntax-case</CODE>, the low-level macro facility
-proposed and implemented by Robert Hieb and R. Kent Dybvig.
-</P>
-<P>
-
-This version is further adapted by Harald Hanche-Olsen
-&lt;hanche @ imf.unit.no&gt; to make it compatible with, and easily usable
-with, SLIB. Mainly, these adaptations consisted of:
-</P>
-<P>
-
-<UL>
-<LI>
-Removing white space from `<TT>expand.pp</TT>' to save space in the
-distribution. This file is not meant for human readers anyway<small>...</small>
-<P>
-
-</P>
-<LI>
-Removed a couple of Chez scheme dependencies.
-<P>
-
-</P>
-<LI>
-Renamed global variables used to minimize the possibility of name
-conflicts.
-<P>
-
-</P>
-<LI>
-Adding an SLIB-specific initialization file.
-<P>
-
-</P>
-<LI>
-Removing a couple extra files, most notably the documentation (but see
-below).
-</UL>
-<P>
-
-If you wish, you can see exactly what changes were done by reading the
-shell script in the file `<TT>syncase.sh</TT>'.
-</P>
-<P>
-
-The two PostScript files were omitted in order to not burden the SLIB
-distribution with them. If you do intend to use <CODE>syntax-case</CODE>,
-however, you should get these files and print them out on a PostScript
-printer. They are available with the original <CODE>syntax-case</CODE>
-distribution by anonymous FTP in
-`<TT>cs.indiana.edu:/pub/scheme/syntax-case</TT>'.
-</P>
-<P>
-
-In order to use syntax-case from an interactive top level, execute:
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(require 'syntax-case)
-<A NAME="IDX149"></A>(require 'repl)
-<A NAME="IDX150"></A>(repl:top-level macro:eval)
-</pre></td></tr></table>See the section Repl (see section <A HREF="slib_7.html#SEC264">7.5.1 Repl</A>) for more information.
-<P>
-
-To check operation of syntax-case get
-`<TT>cs.indiana.edu:/pub/scheme/syntax-case</TT>', and type
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(require 'syntax-case)
-<A NAME="IDX151"></A><A NAME="IDX152"></A>(syncase:sanity-check)
-</pre></td></tr></table><P>
-
-Beware that <CODE>syntax-case</CODE> takes a long time to load -- about 20s on
-a SPARCstation SLC (with SCM) and about 90s on a Macintosh SE/30 (with
-Gambit).
-</P>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC37"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC36"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC38"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.6.1 Notes </H3>
-<!--docid::SEC37::-->
-<P>
-
-All R4RS syntactic forms are defined, including <CODE>delay</CODE>. Along
-with <CODE>delay</CODE> are simple definitions for <CODE>make-promise</CODE> (into
-which <CODE>delay</CODE> expressions expand) and <CODE>force</CODE>.
-</P>
-<P>
-
-<CODE>syntax-rules</CODE> and <CODE>with-syntax</CODE> (described in <CITE>TR356</CITE>)
-are defined.
-</P>
-<P>
-
-<CODE>syntax-case</CODE> is actually defined as a macro that expands into
-calls to the procedure <CODE>syntax-dispatch</CODE> and the core form
-<CODE>syntax-lambda</CODE>; do not redefine these names.
-</P>
-<P>
-
-Several other top-level bindings not documented in TR356 are created:
-<UL>
-<LI>the &quot;hooks&quot; in `<TT>hooks.ss</TT>'
-<LI>the <CODE>build-</CODE> procedures in `<TT>output.ss</TT>'
-<LI><CODE>expand-syntax</CODE> (the expander)
-</UL>
-<P>
-
-The syntax of define has been extended to allow <CODE>(define <VAR>id</VAR>)</CODE>,
-which assigns <VAR>id</VAR> to some unspecified value.
-</P>
-<P>
-
-We have attempted to maintain R4RS compatibility where possible. The
-incompatibilities should be confined to `<TT>hooks.ss</TT>'. Please let us
-know if there is some incompatibility that is not flagged as such.
-</P>
-<P>
-
-Send bug reports, comments, suggestions, and questions to Kent Dybvig
-(dyb @ iuvax.cs.indiana.edu).
-</P>
-<P>
-
-<HR SIZE="6">
-<A NAME="SEC38"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC37"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC39"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.6.2 Note from SLIB maintainer </H3>
-<!--docid::SEC38::-->
-<P>
-
-<CODE>(require 'structure)</CODE>
-</P>
-<P>
-
-<A NAME="IDX153"></A>
-Included with the <CODE>syntax-case</CODE> files was `<TT>structure.scm</TT>'
-which defines a macro <CODE>define-structure</CODE>. I have no
-documentation for this macro; it is not used by any other code in
-SLIB.
-</P>
-<P>
-
-<A NAME="Fluid-Let"></A>
-<HR SIZE="6">
-<A NAME="SEC39"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC38"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC40"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.7 Fluid-Let </H2>
-<!--docid::SEC39::-->
-<P>
-
-<CODE>(require 'fluid-let)</CODE>
-<A NAME="IDX154"></A>
-</P>
-<P>
-
-<A NAME="IDX155"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>fluid-let</B> <I><CODE>(<VAR>bindings</VAR> <small>...</small>)</CODE> <VAR>forms</VAR><small>...</small></I>
-<DD></DL>
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(fluid-let ((<VAR>variable</VAR> <VAR>init</VAR>) <small>...</small>)
- <VAR>expression</VAR> <VAR>expression</VAR> <small>...</small>)
-</pre></td></tr></table><P>
-
-The <VAR>init</VAR>s are evaluated in the current environment (in some
-unspecified order), the current values of the <VAR>variable</VAR>s are saved,
-the results are assigned to the <VAR>variable</VAR>s, the <VAR>expression</VAR>s
-are evaluated sequentially in the current environment, the
-<VAR>variable</VAR>s are restored to their original values, and the value of
-the last <VAR>expression</VAR> is returned.
-</P>
-<P>
-
-The syntax of this special form is similar to that of <CODE>let</CODE>, but
-<CODE>fluid-let</CODE> temporarily rebinds existing <VAR>variable</VAR>s. Unlike
-<CODE>let</CODE>, <CODE>fluid-let</CODE> creates no new bindings; instead it
-<EM>assigns</EM> the values of each <VAR>init</VAR> to the binding (determined
-by the rules of lexical scoping) of its corresponding
-<VAR>variable</VAR>.
-</P>
-<P>
-
-<A NAME="Yasos"></A>
-<HR SIZE="6">
-<A NAME="SEC40"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC39"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC41"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.8 Yasos </H2>
-<!--docid::SEC40::-->
-<P>
-
-<CODE>(require 'oop)</CODE> or <CODE>(require 'yasos)</CODE>
-<A NAME="IDX156"></A>
-<A NAME="IDX157"></A>
-</P>
-<P>
-
-`Yet Another Scheme Object System' is a simple object system for Scheme
-based on the paper by Norman Adams and Jonathan Rees: <CITE>Object
-Oriented Programming in Scheme</CITE>, Proceedings of the 1988 ACM Conference
-on LISP and Functional Programming, July 1988 [ACM #552880].
-</P>
-<P>
-
-Another reference is:
-</P>
-<P>
-
-Ken Dickey.
-&lt;A HREF=&quot;ftp://ftp.cs.indiana.edu/pub/scheme-repository/doc/pubs/swob.txt&quot;&gt;
-Scheming with Objects
-&lt;/A&gt;
-<CITE>AI Expert</CITE> Volume 7, Number 10 (October 1992), pp. 24-33.
-</P>
-<P>
-
-<TABLE BORDER="0" CELLSPACING="0">
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC41">3.8.1 Terms</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Definitions and disclaimer.</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC42">3.8.2 Interface</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">The Yasos macros and procedures.</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC43">3.8.3 Setters</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Dylan-like setters in Yasos.</TD></TR>
-<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_3.html#SEC44">3.8.4 Examples</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Usage of Yasos and setters.</TD></TR>
-</TABLE>
-<P>
-
-<A NAME="Yasos terms"></A>
-<HR SIZE="6">
-<A NAME="SEC41"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC40"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC42"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC40"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.8.1 Terms </H3>
-<!--docid::SEC41::-->
-<P>
-
-</P>
-<DL COMPACT>
-<DT><EM>Object</EM>
-<DD>Any Scheme data object.
-<P>
-
-</P>
-<DT><EM>Instance</EM>
-<DD>An instance of the OO system; an <EM>object</EM>.
-<P>
-
-</P>
-<DT><EM>Operation</EM>
-<DD>A <VAR>method</VAR>.
-</DL>
-<P>
-
-</P>
-<DL COMPACT>
-<DT><EM>Notes:</EM>
-<DD>The object system supports multiple inheritance. An instance can
-inherit from 0 or more ancestors. In the case of multiple inherited
-operations with the same identity, the operation used is that from the
-first ancestor which contains it (in the ancestor <CODE>let</CODE>). An
-operation may be applied to any Scheme data object--not just instances.
-As code which creates instances is just code, there are no <EM>classes</EM>
-and no meta-<VAR>anything</VAR>. Method dispatch is by a procedure call a la
-CLOS rather than by <CODE>send</CODE> syntax a la Smalltalk.
-<P>
-
-</P>
-<DT><EM>Disclaimer:</EM>
-<DD>There are a number of optimizations which can be made. This
-implementation is expository (although performance should be quite
-reasonable). See the L&amp;FP paper for some suggestions.
-</DL>
-<P>
-
-<A NAME="Yasos interface"></A>
-<HR SIZE="6">
-<A NAME="SEC42"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC41"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC43"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC40"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.8.2 Interface </H3>
-<!--docid::SEC42::-->
-<P>
-
-<A NAME="IDX158"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>define-operation</B> <I><CODE>(</CODE>opname self arg <small>...</small><CODE>)</CODE> <VAR>default-body</VAR></I>
-<DD>Defines a default behavior for data objects which don't handle the
-operation <VAR>opname</VAR>. The default behavior (for an empty
-<VAR>default-body</VAR>) is to generate an error.
-</DL>
-<P>
-
-<A NAME="IDX159"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>define-predicate</B> <I>opname?</I>
-<DD>Defines a predicate <VAR>opname?</VAR>, usually used for determining the
-<EM>type</EM> of an object, such that <CODE>(<VAR>opname?</VAR> <VAR>object</VAR>)</CODE>
-returns <CODE>#t</CODE> if <VAR>object</VAR> has an operation <VAR>opname?</VAR> and
-<CODE>#f</CODE> otherwise.
-</DL>
-<P>
-
-<A NAME="IDX160"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>object</B> <I><CODE>((<VAR>name</VAR> <VAR>self</VAR> <VAR>arg</VAR> <small>...</small>) <VAR>body</VAR>)</CODE> <small>...</small></I>
-<DD>Returns an object (an instance of the object system) with operations.
-Invoking <CODE>(<VAR>name</VAR> <VAR>object</VAR> <VAR>arg</VAR> <small>...</small></CODE> executes the
-<VAR>body</VAR> of the <VAR>object</VAR> with <VAR>self</VAR> bound to <VAR>object</VAR> and
-with argument(s) <VAR>arg</VAR><small>...</small>.
-</DL>
-<P>
-
-<A NAME="IDX161"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>object-with-ancestors</B> <I><CODE>((</CODE>ancestor1 init1<CODE>)</CODE> <small>...</small><CODE>)</CODE> operation <small>...</small></I>
-<DD>A <CODE>let</CODE>-like form of <CODE>object</CODE> for multiple inheritance. It
-returns an object inheriting the behaviour of <VAR>ancestor1</VAR> etc. An
-operation will be invoked in an ancestor if the object itself does not
-provide such a method. In the case of multiple inherited operations
-with the same identity, the operation used is the one found in the first
-ancestor in the ancestor list.
-</DL>
-<P>
-
-<A NAME="IDX162"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>operate-as</B> <I>component operation self arg <small>...</small></I>
-<DD>Used in an operation definition (of <VAR>self</VAR>) to invoke the
-<VAR>operation</VAR> in an ancestor <VAR>component</VAR> but maintain the object's
-identity. Also known as &quot;send-to-super&quot;.
-</DL>
-<P>
-
-<A NAME="IDX163"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>print</B> <I>obj port</I>
-<DD>A default <CODE>print</CODE> operation is provided which is just <CODE>(format
-<VAR>port</VAR> <VAR>obj</VAR>)</CODE> (see section <A HREF="slib_4.html#SEC53">4.2 Format (version 3.0)</A>) for non-instances and prints
-<VAR>obj</VAR> preceded by `<SAMP>#&lt;INSTANCE&gt;</SAMP>' for instances.
-</DL>
-<P>
-
-<A NAME="IDX164"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>size</B> <I>obj</I>
-<DD>The default method returns the number of elements in <VAR>obj</VAR> if it is
-a vector, string or list, <CODE>2</CODE> for a pair, <CODE>1</CODE> for a character
-and by default id an error otherwise. Objects such as collections
-(see section <A HREF="slib_7.html#SEC194">7.1.9 Collections</A>) may override the default in an obvious way.
-</DL>
-<P>
-
-<A NAME="Setters"></A>
-<HR SIZE="6">
-<A NAME="SEC43"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC42"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC44"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC40"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.8.3 Setters </H3>
-<!--docid::SEC43::-->
-<P>
-
-<EM>Setters</EM> implement <EM>generalized locations</EM> for objects
-associated with some sort of mutable state. A <EM>getter</EM> operation
-retrieves a value from a generalized location and the corresponding
-setter operation stores a value into the location. Only the getter is
-named -- the setter is specified by a procedure call as below. (Dylan
-uses special syntax.) Typically, but not necessarily, getters are
-access operations to extract values from Yasos objects (see section <A HREF="slib_3.html#SEC40">3.8 Yasos</A>).
-Several setters are predefined, corresponding to getters <CODE>car</CODE>,
-<CODE>cdr</CODE>, <CODE>string-ref</CODE> and <CODE>vector-ref</CODE> e.g., <CODE>(setter
-car)</CODE> is equivalent to <CODE>set-car!</CODE>.
-</P>
-<P>
-
-This implementation of setters is similar to that in Dylan(TM)
-(<CITE>Dylan: An object-oriented dynamic language</CITE>, Apple Computer
-Eastern Research and Technology). Common LISP provides similar
-facilities through <CODE>setf</CODE>.
-</P>
-<P>
-
-<A NAME="IDX165"></A>
-</P>
-<DL>
-<DT><U>Function:</U> <B>setter</B> <I>getter</I>
-<DD>Returns the setter for the procedure <VAR>getter</VAR>. E.g., since
-<CODE>string-ref</CODE> is the getter corresponding to a setter which is
-actually <CODE>string-set!</CODE>:
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define foo &quot;foo&quot;)
-((setter string-ref) foo 0 #\F) ; set element 0 of foo
-foo => &quot;Foo&quot;
-</pre></td></tr></table></DL>
-<P>
-
-<A NAME="IDX166"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>set</B> <I>place new-value</I>
-<DD>If <VAR>place</VAR> is a variable name, <CODE>set</CODE> is equivalent to
-<CODE>set!</CODE>. Otherwise, <VAR>place</VAR> must have the form of a procedure
-call, where the procedure name refers to a getter and the call indicates
-an accessible generalized location, i.e., the call would return a value.
-The return value of <CODE>set</CODE> is usually unspecified unless used with a
-setter whose definition guarantees to return a useful value.
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>(set (string-ref foo 2) #\O) ; generalized location with getter
-foo => &quot;FoO&quot;
-(set foo &quot;foo&quot;) ; like set!
-foo => &quot;foo&quot;
-</pre></td></tr></table></DL>
-<P>
-
-<A NAME="IDX167"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>add-setter</B> <I>getter setter</I>
-<DD>Add procedures <VAR>getter</VAR> and <VAR>setter</VAR> to the (inaccessible) list
-of valid setter/getter pairs. <VAR>setter</VAR> implements the store
-operation corresponding to the <VAR>getter</VAR> access operation for the
-relevant state. The return value is unspecified.
-</DL>
-<P>
-
-<A NAME="IDX168"></A>
-</P>
-<DL>
-<DT><U>Procedure:</U> <B>remove-setter-for</B> <I>getter</I>
-<DD>Removes the setter corresponding to the specified <VAR>getter</VAR> from the
-list of valid setters. The return value is unspecified.
-</DL>
-<P>
-
-<A NAME="IDX169"></A>
-</P>
-<DL>
-<DT><U>Syntax:</U> <B>define-access-operation</B> <I>getter-name</I>
-<DD>Shorthand for a Yasos <CODE>define-operation</CODE> defining an operation
-<VAR>getter-name</VAR> that objects may support to return the value of some
-mutable state. The default operation is to signal an error. The return
-value is unspecified.
-</DL>
-<P>
-
-<A NAME="Yasos examples"></A>
-<HR SIZE="6">
-<A NAME="SEC44"></A>
-<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
-<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC43"> &lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC21"> &lt;&lt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_3.html#SEC40"> Up </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_4.html#SEC45"> &gt;&gt; </A>]</TD>
-<TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <TD VALIGN="MIDDLE" ALIGN="LEFT"> &nbsp; <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> 3.8.4 Examples </H3>
-<!--docid::SEC44::-->
-<P>
-
-<TABLE><tr><td>&nbsp;</td><td class=example><pre>;;; These definitions for PRINT and SIZE are
-;;; already supplied by
-(require 'yasos)
-
-(define-operation (print obj port)
- (format port
- (if (instance? obj) &quot;#&lt;instance&gt;&quot; &quot;~s&quot;)
- obj))
-
-(define-operation (size obj)
- (cond
- ((vector? obj) (vector-length obj))
- ((list? obj) (length obj))
- ((pair? obj) 2)
- ((string? obj) (string-length obj))
- ((char? obj) 1)
- (else
- (slib:error &quot;Operation not supported: size&quot; obj))))
-
-(define-predicate cell?)
-(define-operation (fetch obj))
-(define-operation (store! obj newValue))
-
-(define (make-cell value)
- (object
- ((cell? self) #t)
- ((fetch self) value)
- ((store! self newValue)
- (set! value newValue)
- newValue)
- ((size self) 1)
- ((print self port)
- (format port &quot;#&lt;Cell: ~s&gt;&quot; (fetch self)))))
-
-(define-operation (discard obj value)
- (format #t &quot;Discarding ~s~%&quot; value))
-
-(define (make-filtered-cell value filter)
- (object-with-ancestors
- ((cell (make-cell value)))
- ((store! self newValue)
- (if (filter newValue)
- (store! cell newValue)
- (discard self newValue)))))
-
-(define-predicate array?)
-(define-operation (array-ref array index))
-(define-operation (array-set! array index value))
-
-(define (make-array num-slots)
- (let ((anArray (make-vector num-slots)))
- (object
- ((array? self) #t)
- ((size self) num-slots)
- ((array-ref self index)
- (vector-ref anArray index))
- ((array-set! self index newValue)
- (vector-set! anArray index newValue))
- ((print self port)
- (format port &quot;#&lt;Array ~s&gt;&quot; (size self))))))
-
-(define-operation (position obj))
-(define-operation (discarded-value obj))
-
-(define (make-cell-with-history value filter size)
- (let ((pos 0) (most-recent-discard #f))
- (object-with-ancestors
- ((cell (make-filtered-call value filter))
- (sequence (make-array size)))
- ((array? self) #f)
- ((position self) pos)
- ((store! self newValue)
- (operate-as cell store! self newValue)
- (array-set! self pos newValue)
- (set! pos (+ pos 1)))
- ((discard self value)
- (set! most-recent-discard value))
- ((discarded-value self) most-recent-discard)
- ((print self port)
- (format port &quot;#&lt;Cell-with-history ~s&gt;&quot;
- (fetch self))))))
-
-(define-access-operation fetch)
-(add-setter fetch store!)
-(define foo (make-cell 1))
-(print foo #f)
-=> &quot;#&lt;Cell: 1&gt;&quot;
-(set (fetch foo) 2)
-=>
-(print foo #f)
-=> &quot;#&lt;Cell: 2&gt;&quot;
-(fetch foo)
-=> 2
-</pre></td></tr></table><P>
-
-<A NAME="Textual Conversion Packages"></A>
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-<FONT SIZE="-1">
-This document was generated
-by <I>Steve Langasek</I> on <I>January, 10 2005</I>
-using <A HREF="http://texi2html.cvshome.org"><I>texi2html</I></A>
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