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From: jaffer@zurich.ai.mit.edu (Aubrey Jaffer)
Newsgroups: comp.lang.scheme
Subject: Re: Logic does not Apply
Message-ID: <JAFFER.91Apr30124710@kleph.ai.mit.edu>
Date: 30 Apr 91 16:47:10 GMT
References: <9104300906.aa04392@mc.lcs.mit.edu>
Sender: news@ai.mit.edu
Organization: M.I.T. Artificial Intelligence Lab.
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In-reply-to: STCS8004%IRUCCVAX.UCC.IE@mitvma.mit.EDU's message of 30 Apr 91 12:36:00 GMT

> 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'.
 
The problem you are having here is that `and' and `or' are poorly
named control structures.  What you want are `and?' and `or?' anyway
since tests are supposed to end with `?'.

(define (and? . args)
        (cond ((null? args) #t)
              ((car args) (apply and? (cdr args)))
              (else #f)))

(define (or? . args)
        (cond ((null? args) #f)
              ((car args) #t)
              (else (apply or? (cdr args)))))