Re: EQness of functions

[Jeff Dalton <jeff%aiai.edinburgh.ac.uk@NSS.Cs.Ucl.AC.UK>]

> The case of
>  (let ((f #'(lambda ...)))
>       (eq f f))
> has no bearing on the issue of whether (eq f #'eq) is valid.  #'eq means
> (function eq), which may or may not result in something being done at
> run time to evaluate it; f is a variable reference whose value has already
> "been evaluated" at some prior time.  (eq f f) ought to always be true,
> modulo some kinds of number-optimization.

It is clear at least they we are not understanding each other.
I will try again nonetheless.  The problem may be that I am
talking about what FUNCTION should be and you seem to be talking
about what it is.

I want #'F to be a reference in the function namespace just as
plain F is a reference in the value namespace.

Consider the following in Scheme:

   (let ((f (lambda ...)))
     (eq f f))

This will return true.  In Common Lisp, I might write it as:

  (let ((f #'(lambda ...)))
    (eq f f))

but I might prefer:

  (flet ((f ...)) (eq #'f #'f))

I do not think that this additional transformation (into FLET) should
introduce any new uncertainty w.r.t. EQ -- because #'F, like F, is
just a reference (whose value has already been evaluated).  The
relevance of the LET example is that it and the FLET version should
(in my view) be equivalent.

Put another way, I suggest that FUNCTION should be interpeted as
more or less a syntactic marker as in

    <form> ::= ... | (FUNCTION <function>) | ...

    <function> ::= <identifier> | (LAMBDA <lambda list> <form>*)

That is, (LAMBDA ...) in, say, ((LAMBDA ...) ...) has as its value
a function; (LAMBDA ...) in (FUNCTION (LAMBDA ...)) is interpreted
in more or less the same way; but in (... (LAMBDA ...) ...) it is not
[it's interpreted as a call to the (non-)function LAMBDA].  So in
the <identifier> case, FUNCTION simply indicates that the identifier
is a function name, not a variable.

In other words, I do not think of FUNCTION as an operation that
constructs a value -- it's not like LIST or MAKE-SYMBOL.  Furthermore,
I am not saying that Common Lisp currently treats FUNCTION in the way
I prefer -- I am saying that (in my opinion) it should.

Finally, recent messages have shown that the "may make a new object
each time" view of (FUNCTION <identifier>) provides some freedom that
can be exploited in various ways.  Whether this freedom is important
enough to determine the semantics is less clear.

I hope everyone isn't *too* tired of this.

Cheers,
Jeff