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From: yodaiken@chelm.cs.umass.edu (victor yodaiken)
Newsgroups: comp.lang.misc
Subject: Re: Dynamic typing (part 31,497)
Message-ID: <29350@dime.cs.umass.edu>
Date: 16 Apr 91 15:04:12 GMT
References: <1883@optima.cs.arizona.edu>
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Reply-To: yodaiken@chelm.cs.umass.edu (victor yodaiken)
Organization: University of Massachusetts, Amherst
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In article <1883@optima.cs.arizona.edu> gudeman@cs.arizona.edu (David Gudeman) writes:
>In article  <8742@skye.cs.ed.ac.uk> Nick Rothwell writes:
>]
>]Now, using such general terms as "function" and "sequence" in a mathematical
>]context, I assumed your were implying a homogeneous list. If you're assuming
>]heterogeneous sequences, then the kind of mathematics you're dealing with
>]gets more complicated than I assumed. I think.
>
>Why would you assume that?  Math makes no distinction between
>homogenous and heterogeneous lists.  What complication are you talking
>about?  It is trivial to define a heterogeneous list in math:
>
>Let S be the sequence beginning with S[1] defined as follows:
>  if i is odd then S[i] = i
>  if i is even then S[i] = {i, i-1}
>
>It is equally trivial to define a function to act on heterogenous
>elements:
>
>Let f x be defined as follows:
>  if x is an integer then x
>  else if x is a set then the min element of x
>
>All of this can be programmed directly in a language with dynamic
>typing and requires extra effort in a language with static typing.
>My main criterion for the expresiveness of a language is "does it let
>me say what I want to directly, instead of making me work around
>limitations in the language?"
>--


Your example seems to involve the use of type definitions. If I now write
f((1,2,3,4)) the compiler should be able to inform me that I have
attempted to apply "f" to a list, but "f" is only defined on sets and
integers.