Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!aiai!jeff
From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.lisp
Subject: Re: FUNCALL question
Message-ID: <1666@skye.ed.ac.uk>
Date: 1 Feb 90 20:26:43 GMT
References: <3277@accuvax.nwu.edu> <1990Jan28.175437.19293@hellgate.utah.edu> <1655@skye.ed.ac.uk> <386@forsight.Jpl.Nasa.Gov>
Reply-To: jeff@aiai.UUCP (Jeff Dalton)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 47

In article <386@forsight.Jpl.Nasa.Gov> gat@robotics.Jpl.Nasa.Gov (Erann Gat) writes:
>In article <1655@skye.ed.ac.uk>, jeff@aiai.ed.ac.uk (Jeff Dalton) writes:
>> Indeed, an identifier can be associated with two values at once,
>> one when it's interpreted as a function name, the other when it's
>> interpreted as a variable.  Erann Gat made the mistake of calling
>> these two interpretations the symbol-function and symbol-value
>> when those terms are properly applied only to symbols (acting
>> as global variables and function names).  Local variables and
>> function names don't have symbol-values or symbol-functions in
>> that sense.  

>I want to thank Jeff Dalton for coming to my defense.  However, the
>above is totally incorrect (said with a smile).  Temporary variables
>do have value and function bindings.  That is why there are LET and
>FLET forms in CL.  For example:

No, you have it wrong -- this time.  But it's because I failed to make
some things clear.

I tried to be careful to say "identifier" when I was talking about a
name in a program and "variable" and "function name" for the two
possible interpretations of identifiers (possible in the contexts we
were interested in, that is).  In this terminology, a _variable_
doesn't have both a function and value binding, but a single name
might have both, in a sense, because it's being used as both a
variable and a function name.

We could shift terminology, however, and say that a variable can
have both a value and a function binding (as you say above).  I
wasn't trying to disagree with you there.

However, once you say "symbol-value" and "symbol-function" people may
well assume you're talking about _symbols_ (the data objects) and the
associated values obtained by the Common Lisp functions SYMBOL-VALUE
and SYMBOL-FUNCTION.  Indeed, I thought people were reading you that
way.

The problem with talking this way is that local variables might not
be associated with symbols at all -- after compilation, for example.
And, in any case, the functions SYMBOL-VALUE and SYMBOL-FUNCTION can't
look at local variables.

Anyway, that's the "sense" I had in mind when I wrote "local variables
and function names don't have symbol-values or symbol-functions in
that sense."

-- Jeff