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Re: (list) and '(list)
From: |
A Soare |
Subject: |
Re: (list) and '(list) |
Date: |
Fri, 27 Apr 2007 12:37:59 +0200 (CEST) |
> The following message is a courtesy copy of an article
> that has been posted to gmane.emacs.help as well.
>
> A Soare <alinsoar@voila.fr> writes:
>
> > Can somebody tell me if there already is a code that makes the
> > distintion between a list that evaluates as a function like
> >
> > (function ...
> >
> > and between a list that evaluates to itself :
> >
> > '(list ... , and its aliases like (quote (list ... etc
>
> Like the others who responded, it is not clear to me what you want.
>
> Lisp normally reads code and then evaluates (evals) it. During
> reading, it performs some (few) conversions such as 'foo to (quote
> foo). During evaluation, the magic happens:
>
> - If we are looking at a number or a string, return that number or
> string. (Numbers and strings are said to be self-evaluating because
> they evaluate to themselves.) If we are looking at some special
> symbols (like t and nil), return those values. (t and nil are also
> self-evaluating.)
>
> - If we are looking at a list, look at the first element of the list.
> If it is a function, then eval all other elements of the list, then
> use the results as arguments to the function (call the function).
> Then return the result of the function call.
>
> - The first element can also be a special form. In this case, the
> other elements of the list are NOT evaled but instead passed to the
> special form verbatim.
>
> Popular special forms: defun, quote, if, setq
>
> So in a strict sense, what you can do is:
>
> (setq unevaled (read STREAM))
> (setq evaled (eval unevaled))
> (equal unevaled evaled)
That is what I wanted to know. Giving a string/[part of a buffer] that
represents a LISP code, to say if a list inside it defines a function or a
symbol (that evaluates to itself).
That code solves my problem. Thank you very much.
Alin Soare.