Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!milton!ogicse!pdxgate!qiclab!percy!data!kend
From: kend@data.UUCP (Ken Dickey)
Newsgroups: comp.lang.scheme
Subject: Re: Logic does not Apply
Message-ID: <484@data.UUCP>
Date: 2 May 91 16:14:56 GMT
References: <9104300906.aa04392@mc.lcs.mit.edu>
Organization: Microcosm, Beaverton, OR
Lines: 35

STCS8004%IRUCCVAX.UCC.IE@mitvma.mit.EDU writes:

>The title says it all, but some elaboration is perhaps in order!

>One might expect (naively?) that
>     (apply bin-op (list item1 item2))  =  (bin-op  item1 item2)
>for *all* bin-ops, provided that bin-op's arguments are compatible with it.
>But it is not so, since instead of the expected
>     (apply and '(#f #t)) --> #f
>one gets some  grumble that either 'and' is an  undefined variable or it is
>not the right kind of parameter-1 to 'apply'.

I suggest that the problem is not one of "logic", but of using a similar syntax
to express both procedure calls and evaluation rules.  {The number of special
forms in Scheme is, after all, quite small}.

From your comments, you would expect the following to "work":
	(apply if    (list a b c))
	(apply begin (list a b c))
	(apply set!  (list a b))
	(apply let   (list ((a 1)(b 2) (+ a b))))
	...

(apply a b) is *not* equivalent to (eval (cons 'a b)) because of
differences in order of evaluation.


>  Why shouldn't 'and' and 'or' be first class citizens of Scheme?

Why are special forms not applications?  Because they are very useful
is expressing another level of computational specification: how
evaluation is to proceed.


-Ken Dickey					kend@data.uucp