Re: Proposal for syntax changes in Curry

From: Wolfgang Lux <lux_at_helios.uni-muenster.de>
Date: Fri, 23 Oct 1998 13:37:22 +0100

Michael Hanus wrote:
> Wolfgang Lux wrote:
> > First I do not see the reason why you want to restrict the expression
> > inside a
> >
> > let ... free in exp
> >
> > to the type of constraint.
>
> This restriction is due to semantical reasons. Since "let...free"
> corresponds to existential quantification, it is natural to
> have it in constraints, but I do not know what is the semantics
> of a term like "there exists an x such that x+2".

I don't see it either for that term, but what about:

  let xs = [1,2,3] in let ys, y in append ys y =:= xs => y

where append is the flexible version of (++) and => would be defined as

  c => x | c == succeeded = x

I think there is an obvious interpretation for that expression, viz. 3,
but this is no longer legal because the whole expression is not of type
constraint.

Regards
Wolfgang

--
Wolfgang Lux				  Phone: +49-251-83-38263
Institut fuer Wirtschaftinformatik	    FAX: +49-251-83-38259
Universitaet Muenster		Email: lux_at_helios.uni-muenster.de
Received on Fri Oct 23 1998 - 14:45:00 CEST

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