Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!hellgate.utah.edu!defmacro.utah.edu!moore
From: moore%defmacro.utah.edu@cs.utah.edu (Tim Moore)
Newsgroups: comp.lang.lisp
Subject: Re: AKCL dynamic symbol table - HELP needed
Message-ID: <1991Apr3.134053.8574@hellgate.utah.edu>
Date: 3 Apr 91 20:40:53 GMT
References: <8693@ucdavis.ucdavis.edu>
Organization: University of Utah CS Dept
Lines: 36

In article <8693@ucdavis.ucdavis.edu> gfink@iris.UCDavis.EDU (George Fink) writes:
>I am working on a program to be written in AKCL, and I wish to have 
>dynamically created lambda expressions which have some sort of static
>symbol information specific to the expression.  Is there a simple
>way/package to implement this, or is the best way to manually create a
>self-modifying a-list (or similar structure) to store the permanent
>information? 

The best way to do this is to use closures.

>For example, say I have the following expression (excuse syntactic errors):`
>
>(lambda () (let ((c 0)) (setq c (1+ c)) (if (= c 10) (do something))))

You would want to write that as 
(let ((c 0))
  #'(lambda ()
      (setq c (1+ c))
      (if (= c 10)
	  (do-something))))

This expression returns a lambda that when called will do what you want to do.

>between calls.  But I am going to be creating these lambda expressions
>on the fly,
>albiet in some standard formats.

I'm not sure what you mean by this. The above expression will create a
fresh lambda every time it is evaluated, with a new "cell" for c. If
you are contemplating consing up lambda expressions and EVALing them,
you might want to rethink your approach. 

-- 
Tim Moore                    moore@cs.utah.edu {bellcore,hplabs}!utah-cs!moore
"Ah, youth. Ah, statute of limitations."
		-John Waters