Merge branch 'master' of ssh://animus.robocracy.org/srv/git/knowledge

4 files changed, 193 insertions, 0 deletions

diff --git a/software/functional programming b/software/functional programming
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+===================================
+Functional Programming
+===================================
+
+Recursion
+--------------
+**Partial** functions can recurse endlessly over a finite input. **Total**
+functions will terminate/halt over a finite input. (TODO: check this
+definition)
+
+Collectors
+--------------
+The collector concept/pattern/paradigm is the one I am least familiar with
+in functional programming.
+
+My current understanding is that they essentially allow allow recursive
+functions to maintain something like state by wrapping immutable functions
+or variables in layer after layer of functions and just holding on to
+the outermost layer. For instance, the typical way to write a ``length``
+function in python would be::
+
+>>> def how-long(x):
+>>>     l = 0
+>>>     while x.has_next()
+>>>         l = l+1;
+>>>         x.pop()
+>>>     return l
+
+Using recursion, we could do::
+
+>>> def how-long-recurse(x):
+>>>     if x.has_next()
+>>>         x.pop()
+>>>         return how-long-recurse(x) + 1
+>>>     else
+>>>         return 0
+
+Using the collector paradigm, we could do::
+
+>>> def add1(x): return a+1;
+>>> def how-long-col(x, col):
+>>>     if x.has_next()
+>>>         return col(0)
+>>>     else
+>>>         x.pop()
+>>>         return how-long-col(x, lambda a: col(add1(a)))
+
+The first two ways, the plus one operation is actually executed at any given
+time, while with the collector implementation we're really creating a
+function step by step which will give the answer at the end when it is all
+executed.
+
diff --git a/software/git b/software/git
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+=======================
+Git
+=======================
+
+Quick tip: when you have ``.gitignore`` ignoring everything (with a ``*`` 
+entry), you need to use ``git-update-index --add FILE`` to actually add the
+file, instead of just ``git-add FILE``.
diff --git a/software/ruby b/software/ruby
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+==================
+Ruby
+==================
+
+.. note:: This information is very rough, it's mostly my notes about what is 
+    different about Ruby syntax compared to similar modern interpreted 
+    pan-paradigm languages like Python.
+
+A unique intro to ruby is `"Why's Poignant Guide to Ruby"`__, a web-comic-y 
+short free online book by why the luck stiff. The more serious reference is 
+the "pickax" book.
+
+__ http://poignantguide.net/
+
+Blocks
+---------
+Blocks of code can be passed to functions, making ruby code more of a first
+order data type.
+
+Ranges 
+----------
+
+>>> 2..7                # => 2..7
+>>> (2..7).to_a         # => [2, 3, 4, 5, 6, 7]
+>>> (2...7).to_a        # => [2, 3, 4, 5, 6]
+>>> ('e'..'h').to_a     # => ["e", "f", "g", "h"]
+
+Control Structures
+--------------------
+Can use ``if`` after a statement::
+
+>>> a = c if c > b
+
+Along with the usual ``break`` and ``next``, there is ``redo`` which redoes
+the current loop (initial conditions may have been changed).
+
+
+Boolean Operators
+--------------------
+Anything that is not ``nill`` or ``false`` is true. To force interpretation
+as boolean, use ``!!`` (not not)::
+
+>>> !!(nil)     # => false
+>>> !!(true)    # => true 
+>>> !!('')      # => true 
+>>> !!(0)       # => true 
+>>> !!({})      # => true 
+
+
+Misc
+----------------
+Can use nasty Perl style regular expression stuff::
+
+>>> re1 = /\d+/
+>>> "There are 5 kilos of chunky bacon on the table!" =~ re1 # => 10, the index
+>>> $~ # =>         #<MatchData:0xb7c36754> 
+>>> $~.pre_hash     # => "There are "
+
+Also $1, $2, etc.
+
+The "splat operator", '*', either collects or expands extra arguments depending
+on syntax (I think this is kind of icky)::
+
+>>> a, b = 1, 2, 3, 4       # a=1, b=2
+>>> a, *b = 1, 2, 3, 4      # a=1, b=[2,3,4] 
+>>> c, d = 5, [6, 7, 8]     # c=5, d=[6,7,8]
+>>> c, d = 5, *[6, 7, 8]    # c=5, b=6
diff --git a/software/scheme b/software/scheme
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+==================
+Scheme
+==================
+
+``mit-scheme`` with the ``scmutils`` package is assumed; the command 
+``mechanics`` starts in interactive edwin prompt. 
+
+See also notes on `The Little Schemer </k/books/littleschemer/>`__.
+
+Scheme Implementations
+-----------------------
+
+Very partial list, mostly just the ones which are interesting to me.
+
+MIT/GNU Scheme
+    The 7.9.0 release (last stable as of 01/01/2009) is not R5RS compatible,
+    and is generally a pain in the ass to compile on new systems. The 9.0
+    release should be easier to compile and distribute because it will use
+    a C compiler to bootstrap (true?).
+
+SCM
+    SCM is a fairly minimal, very small footprint R5RS-compatible 
+    implementation. Apparently very portable and easy to compile. Includes
+    the Hobbit compiler. Part of the GNU project, maintained at MIT?
+
+SIOD
+    SIOD (scheme in one day) is a super small (75k binary?) Scheme 
+    implementation.
+
+Coding in ``edwin``
+-----------------------
+
+..note: this section should be spun off as emacs. edwin is essentially a 
+    scheme version of emacs. See this 
+    `http://static.bryannewbold.com/mirror/sheets/emacs.pdf`:emacs cheatsheet:
+
+Common keyboard commands (usually 'M' is alt button, 'C' is ctrl, and 'S' is 
+meta/super/"windows"):
+
+=========   ====================================================================
+C-x C-f     Open a file, or create a new one
+C-x C-s     Save the file
+C-x k       Kill (close) a buffer
+C-x C-c     Exit the editor
+C-g         Abort a command
+C-x C-e     Evaluate the previous expression
+M-z         Evaluate the surrounding expression
+M-o         Evaluate the entire buffer (everything)
+C-c C-c     Kill evaluation after an error
+C-y         Paste (yank)
+C-x 2       Split screen vertically
+C-x 5       Split screen horizontally
+C-x o       Switch to next buffer window
+C-x 1       Return to non-split screen
+M-x         Enter a command by name in minibuffer (use tab to complete)
+C-x C-b     Show buffer menu
+C-x b       Select buffer
+C-x u       Undo
+C-y         Paste
+=========   ====================================================================
+
+Scope
+--------------
+
+``set!`` looks up a symbol name and permanently changes the first value it comes
+across. ``let`` (and ``letrec``) create a new symbol with the given value.
+But wait, you need a ``lambda`` block to make everything work?