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Newsgroups: comp.lang.misc
Subject: Re: Dynamic typing (part 3)
Message-ID: <1991Mar28.025541.9078@comp.vuw.ac.nz>
From: brian@comp.vuw.ac.nz (Brian Boutel)
Date: Thu, 28 Mar 1991 02:55:41 GMT
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References: <602@optima.cs.arizona.edu> <2400035@otter.hpl.hp.com> <1991Mar27.161304.17666@daffy.cs.wisc.edu>
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In article <1991Mar27.161304.17666@daffy.cs.wisc.edu>,
quale@saavik.cs.wisc.edu (Douglas E. Quale) writes:
|> >typed languages are generally half to a tenth the size of programs
|> in
|> >statically typed languages"  Dan Bernstein reasonably writes back.
|> >
|> >] I don't believe you. Give an example.
|> >
|> 
|> In Common Lisp,
|> 
|> (defun compose (f g)
|>   (lambda (&rest) (funcall f (apply g &rest))))
|> 
|> I think it looks better in Scheme,
|> 
|> (define (compose f g)
|>   (lambda x (f (apply g x))))
|> 
|> These definitions use dynamic typing to obtain polymorphism.
|> 
|> I think it would take at least two orders of magnitude (probably
|> three) to
|> do this in C.
|> 
|> -- Doug Quale
|> quale@saavik.cs.wisc.edu

Why do you think this is dynamic typing? Definitions parallel to this
exist in statically typed languages like Haskell and ML.

In Haskell, write

 compose f g = \ x -> f (g x)

This is even shorter than the lisp/scheme versions. Its type (in the
normal Hindley/Milner type system) is

(forall T1, T2, T3), (T1->T2) -> (T3->T1) -> (T3->T2)

This is polymorphic because any types can be (consistantly) substituted
for the type variables T1,T2 and T3.

This typing can be inferred at compile time, which is what is meant by static.

So try again.

--brian
 
-- 
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