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---
format: rst
toc: no
...
==================
Scheme
==================
``mit-scheme`` with the ``scmutils`` package is assumed; the command
``mechanics`` starts in interactive edwin prompt.
See also notes on [The Little Schemer](/books/Little+Schemer/).
Scheme Implementations
-----------------------
Very partial list, mostly just the ones which are interesting to me.
Alexey Radul maintains a nice table of R5RS implementation details in various
packages on his [website](http://web.mit.edu/~axch/www/scheme/choices.html).
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
[emacs cheatsheet](http://static.bnewbold.net/mirror/sheets/emacs.pdf)*
Common keyboard commands (usually 'M' is alt button, 'C' is ctrl, and 'S' is
meta/super/"windows"):
--------- --------------------------------------------------------------------
Shortcut Effect
--------- --------------------------------------------------------------------
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
--------- --------------------------------------------------------------------
Command in ``.edwin`` to set Super-TAB to autocomplete scheme variables::
(define-key 'Scheme #\s-tab 'scheme-complete-variable)
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?
Environment/Interpreter Commands
-----------------------------------
``(disk-save filename)`` will save a binary microcode image; an existing
image can be specified with the ``--band`` option at runtime or with
``(disk-restore filename)`` from within the interpreter. Bands are also called
worlds.
"First Class"
------------------
"Procedures as first class objects" is one of the features commonly attributed
to scheme. What does that mean? SICP describes first class objects as those
that can be: named by variables, passed as arguments, returned as results,
and included in data structures.
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