Help understanding Scheme's syntax, procedures and calls

Fran franbarlow at mail.com
Thu Aug 12 22:15:44 CEST 2004


eddie at holyrood.ed.ac.uk (Eddie Corns) wrote in message news:<cffit6$shd$1 at scotsman.ed.ac.uk>...
> franbarlow at mail.com (Fran) writes:
> 
> >I'm trying to understand a functional language code fragment so I can
> >explain its syntax and workings to my non English-speaking background
> >neighbour, who is doing her finals.
>  
> >What in heaven's name is this code fragment intending? (In English
> >prose if possible).
>  
> >It looks like a fragment from a language called "scheme"
>  
> >(define (this n)
> >	(if (=n 0)
> >	         0
> >	          (= n (this (- n 1)))))
> 
> As given this is almost certainly wrong.  The first problem is possibly just a
> transcription error in that (=n 0) should probably be (= n 0).  The second one
> is the that the last line doesn't make sense.  It looks like someone is
> confused about how if statements work.  Since this looks suspiciously like
> homework I'm only giving a hint.  If statements work like
> (if expr1
>     (expr to return if exp1 is true)
>     (expr to return if exp1 is false))
> Since each arm is an expression to evaluate it means you evaluate '=' as a
> function in the last line hence it returns a boolean, which is going to cause
> you grief after a short while.
> 
> >(define (f1 a b)
> >	(if >b a)
> >	       0
> >	       (+ b (f1 a (+ b 1)))))
> 
> This is wrong syntactically (hint: the first expression for the if statement)
> 
> The questions wouldn't make sense until you fixed the functions.
> 
> There is a comp.lang.scheme incidentally.
> 
> Eddie

Thanks for the help. It's not homework but from an old exam paper, but
the girl's English isn't absolutely fluent and I'm looking for a
simple way to explain the expressions and functions.

FRAN



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