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Message from discussion Lisp vs. Scheme
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Joe Marshall  
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 More options Sep 19 2003, 9:38 am
Newsgroups: comp.lang.lisp
From: Joe Marshall <j...@ccs.neu.edu>
Date: Fri, 19 Sep 2003 09:38:42 -0400
Local: Fri, Sep 19 2003 9:38 am
Subject: Re: Lisp vs. Scheme
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g...@jpl.nasa.gov (Erann Gat) writes:
> In article <b295356a.0309181447.44dbe...@posting.google.com>,
> thelif...@gmx.net (thelifter) wrote:

>> Can anyone give a simple example where you do some computational task
>> with Lisp that would be much harder to do with Scheme so that the
>> advantage of Lisp becomes more apparent?

> (defmacro compile-time-factorial (n)
>   (if (numberp n)
>     (if (and (integerp n) (> n 0))
>       (factorial n)
>       (error "Can't take the factorial of ~S" n))
>     (if (or (symbolp n) (listp n))
>       `(factorial ,n)
>       (error "Can't take the factorial of ~S" n))))

> E.

(require (lib "defmacro.ss"))

(defmacro compile-time-factorial (n)

  (define (factorial x)
    (if (zero? x)
        1
        (* x (factorial (sub1 x)))))

  (if (number? n)
      (if (and (integer? n) (> n 0))
          (factorial n)
          (error "Can't take the factorial of " n))
      (if (or (symbol? n) (list? n))
          `(factorial ,n)
          (error "Can't take the factorial of " n))))


 
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