FUNCTION and MACROLET

[NGALL@G.BBN.COM]

    Date: Fri, 2 May 86 17:43:51 pdt
    From: yuasa@kurims.kurims.kyoto-u.junet
    To: Common-Lisp@SU-AI.ARPA
    Message-ID: <8605030043.AA01090@kurims.kyoto-u.junet>
    
    Subject: FUNCTION and MACROLET
    
    To sum up, there are two possibilities:
    
    [A] (MACROLET ((FOO ...)) (FUNCTION FOO)) causes an error, and

    SYMBOL-FUNCTION with non-function symbol also causes an error.
    
    [B] (MACROLET ((FOO ...)) (FUNCTION FOO)) returns some totally random object
    which, when invoked as a function, will cause an error.  SYMBOL-FUNCTION
    with non-function symbol also returns something not a function.

    CLtL supports [B].  Also Guy's proposed clarification seems to support [B].
    However, [B] forces the compiler to INVENT something not a function, and to
    silently generate code that returns the something, although this something is
    totally useless.  Rather, the compiler should cause an error when processing
    the above MACROLET form.  I prefer [A].  As Rob said, the difference of [A]
    and [B] do not matter actually.  In addition, it will be straightforward
    to change an already existing implementation toward [A].  (Indeed, I think
    I could do the change in five minutes for KYOTO!!)
    
    The above discussions (and the discussions of Bob and Nick) are based on
    Nick's assumption that FUNCTION with a symbol should correspond to
    SYMBOL-FUNCTION in sense that a symbol as a variable corresponds
    to SYMBOL-VALUE).  Is this what most people agree with?  Yes, the description
    of FUNCTION in CLtL says
    
	    ...; see SYMBOL-FUNCTION.
    
    The reader of CLtL might see the description of SYMBOL-FUNCTION.  Perhaps
    he would like to say "yes, I saw it... so what?"
    
Nick's assumption is wrong here.  On pg. 32 it says "The result of
evaluating a FUNCTION special form will always be a function."

Thus, even in the current CLtL, FUNCTION and SYMBOL-FUNCTION are
not defined to behave identically in the the case of a symbol that
globally names a macro or special form.

Given that FUNCTION is not defined to work with symbols naming
non-functions and given that MACRO-FUNCTION can be used to assign a
new name to a macro, and given that we probably want it to be illegal
to give a new name to a special form (I think we discussed this aspect
of SYMBOL-FUNCTION once), then I agree that [A] is the best solution
(assuming that "causes an error" does not mean "signal an error" but
merely "is an error").

	-- Nick