Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!ucbvax!hplabs!hplabsb!kirshenb
From: kirshenb@hplabsb.HP.COM (Evan Kirshenbaum)
Newsgroups: comp.lang.misc
Subject: Re: What I'd really like to see in an if-statement...
Message-ID: <5410@hplabsb.HP.COM>
Date: 5 Sep 89 18:16:35 GMT
References: <13359@megaron.arizona.edu> <282@castle.ed.ac.uk> <89723@ti-csl.csc.ti.com>
Reply-To: kirshenb@hplabsb.UUCP (Evan Kirshenbaum)
Organization: Hewlett-Packard Labs, Palo Alto, CA
Lines: 35

In article <89723@ti-csl.csc.ti.com> gateley@m2.UUCP (John Gateley) writes:
>In article <282@castle.ed.ac.uk> db@lfcs.ed.ac.uk (Dave Berry) writes:
>>In article <13359@megaron.arizona.edu> gudeman@arizona.edu (David Gudeman) writes:
>>>In article  <8620@batcomputer.tn.cornell.edu> lacey@batcomputer.tn.cornell.edu (John Lacey) writes:
>>>>In talking about _Real Conditionals_ :), 
>>>>So far, Lisp, Icon, and BCPL have all tried and failed to meet the challenge
>>>
>>>Urr.  I thought both Lisp and Icon succeeded. [...]
>>I agree about Icon, but are you sure about Lisp?  I thought that
>>(< a b) returned either t or nil.  If so, although it can handle
>>cases like (< a b c d), it can't handle (<= (< a b) c).

In scheme, one should be able to do something of the form:

(extend-syntax (order)
  ((order) '#!true)
  ((order a op b more ...)
   (with ((temp (gensym)))
     (let ((temp b))
       (and (op a temp)
            (order temp more ...))))))

which would allow you to write infix relations of the form
   (order a < b >= c != d = e divides f)
This allows any binary operation to be used as an operator, and should
be trivially optimized by the compiler.

Evan Kirshenbaum
    HP Laboratories
    3500 Deer Creek Road, Building 26U
    Palo Alto, CA  94304

    kirshenbaum@hplabs.hp.com
    (415)857-7572