Re: Question about Elisp language abilities (evaluating expr on time of func definition and ability to construct function).

[Oleksandr Gavenko]

30.09.2011 0:33, Oleksandr Gavenko пишет:
> I learn Elisp lang capability. According to
>
> 13.2 Expansion of a Macro Call
>
> section of 'info elisp':
>
> Evaluation of the macro call begins like evaluation of a
> function call except for one crucial difference: the macro
> arguments are the actual expressions appearing in the macro
> call. They are not evaluated before they are given to the
> macro definition.
>
> So Elisp macro executed when func called, but with different algorithm
> of args passing. This allow make "new" language constructions but
> I know about more powerful abilities.
>
>
> Is there any Elisp special form which evaluate args when 'defun' parsed
> (like words which defined with IMMEDIATE marker in Forth prog lang)?
>
> In Forth in time of processing of word definition compiler can pass
> control to interpreter when encounter special word until they decide
> back to compilation process.
>
> So in similar construction exist in Elisp this hypothetical code:
>
> (defun f (x)
> (IMMEDIATE (message "hello!"))
> (1+ x)
> )
>
> on 'f' compilation stage print "hello" and never do this on 'f'
> evaluation.
>
>
> Another question is there ability to construct function on the fly.
> For example:
>
> (GENFUNC get-parser (syntax-tree) (data)
> ...
> )
>
> syntax-tree is a string, data is free argument. When you call
>
> (get-parser "a=a|ab; b=*")
>
> you get function with one argument (remember 'data'?) which constructed
> dynamically and can perform parsing very speedily
> (as 'get-parser' can be more fast then general purpose parser
> as it know 'syntax-tree' on construction stage).
When write previous post I use '(when (x-condp) (defun f (x) x))'
expression.

And recall as I wrote such code half year before to avoid
code duplication in .emacs:

  (defmacro my-defun-rename-symb-tree (name doc func)
    "Travel by TREE and applies FUNC to each symbol."
    `(defun ,name (tree)
       ,doc
       (cond
        ((symbolp tree)
         (,func tree)
         )
        ((listp tree)
         (mapcar ',name tree)
         )
        (t (error "Only tree of symbols allowed."))
        )))

  (my-defun-rename-symb-tree
   my-feature2mode
   "Convert TREE of features to TREE of modes for these features.
  Single symbol allowed."
   (lambda (symb) (intern (concat (symbol-name symb) "-mode"))))

  (my-defun-rename-symb-tree
   my-mode2hook
   "Convert TREE of modes to TREE of hooks for these modes.
  Single symbol allowed."
   (lambda (symb) (intern (concat (symbol-name symb) "-hook")))
   )

So from:

  (defvar my-devel-mode-list '(sh-mode script-mode tcl-mode
    c-mode c++-mode java-mode js-mode))

I can get:

  (defvar my-devel-mode-hook-list (my-mode2hook my-devel-mode-list))

So my both question positively answered.


How about nested defmacro? As you see after evaluating macro interpreter
can create function (by 'defun'). What if defmacro create defmacro?