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From: gudeman@cs.arizona.edu (David Gudeman)
Newsgroups: comp.lang.misc
Subject: Re: Dynamic typing (part 3)
Message-ID: <1707@optima.cs.arizona.edu>
Date: 10 Apr 91 17:13:09 GMT
Sender: news@cs.arizona.edu
Lines: 31

In article  <1991Apr9.110217.10963@mathrt0.math.chalmers.se> Lennart Augustsson writes:
]In article <1593@optima.cs.arizona.edu> gudeman@cs.arizona.edu (David Gudeman) writes:
]>  If f is a function and s is a sequence, then map(f,s) is the
]>  sequence t such that for all i . t[i] = f(s[i]).
]>
]>In a Icon (a dynamically typed language) you could define...
]>
]>Try to write this function in a statically typed language so that it
]>has all the generality of the math and Icon versions.

]Sorry, I can't forget it.  I'll just have to make another plug for
]polymorhic type deduction.  Here's a version of map in Haskell (ML
]would be very similar):
]
]  map f [] = []
]  map f (x:xs) = f x : map f xs

I'm getting really tired of pointing this out: the program above does
not have the full generality of the mathematical or the dynamically
typed version.  This is a point I've made several times on several
Haskell and ML programs, and I wish people would get the idea so I
could stop repeating myself.  The statically typed program only works
on structures in which all elements have the same type -- and only
when the compiler can infer that type.

Type inference has some nice features, but it does _not_ give you the
expressive power of dynamic typing.
--
					David Gudeman
gudeman@cs.arizona.edu
noao!arizona!gudeman