lang/elisp/variables.scm

   1 (define-module (lang elisp variables))
   2
   3 ;;; The only purpose of this module is to provide a place where the
   4 ;;; variables holding Elisp function definitions can be bound to
   5 ;;; symbols.
   6 ;;;
   7 ;;; This can be useful when looking at unmemoized procedure source
   8 ;;; code for Elisp functions and macros.  Elisp function and macro
   9 ;;; symbols get memoized into variables.  When the unmemoizer tries to
  10 ;;; unmemoize a variables, it does so by looking for a symbol that is
  11 ;;; bound to that variable, starting from the module in which the
  12 ;;; function or macro was defined and then trying the interfaces on
  13 ;;; that module's uses list.  If it can't find any such symbol, it
  14 ;;; returns the symbol '???.
  15 ;;;
  16 ;;; Normally we don't want to bind Elisp function definition variables
  17 ;;; to symbols that are visible from the Elisp evaluation module (lang
  18 ;;; elisp base), because they would pollute the namespace available
  19 ;;; to Elisp variables.  On the other hand, if we are trying to debug
  20 ;;; something, and looking at unmemoized source code, it's far more
  21 ;;; informative if that code has symbols that indicate the Elisp
  22 ;;; function being called than if it just says ??? everywhere.
  23 ;;;
  24 ;;; So we have a compromise, which achieves a reasonable balance of
  25 ;;; correctness (for general operation) and convenience (for
  26 ;;; debugging).
  27 ;;;
  28 ;;; 1. We bind Elisp function definition variables to symbols in this
  29 ;;; module (lang elisp variables).
  30 ;;;
  31 ;;; 2. By default, the Elisp evaluation module (lang elisp base) does
  32 ;;; not use (lang elisp variables), so the Elisp variable namespace
  33 ;;; stays clean.
  34 ;;;
  35 ;;; 3. When debugging, a simple (named-module-use! '(lang elisp base)
  36 ;;; '(lang elisp variables)) makes the function definition symbols
  37 ;;; visible in (lang elisp base) so that the unmemoizer can find
  38 ;;; them, which makes the unmemoized source code much easier to read.
  39 ;;;
  40 ;;; 4. To reduce the effects of namespace pollution even after step 3,
  41 ;;; the symbols that we bind are all prefixed with `<elisp' and
  42 ;;; suffixed with `>'.