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Re: [Haskell-cafe] Polymorphic (typeclass) values in a list?

Subject: Re: [Haskell-cafe] Polymorphic (typeclass) values in a list?
From: "Brandon S. Allbery KF8NH"
Date: Fri, 19 Oct 2007 12:31:01 -0400

On Oct 19, 2007, at 12:11 , Sebastian Sylvan wrote:

On 19/10/2007, Kalman Noel <[email protected]> wrote:

   data ExistsNumber = forall a. Num a => Number a

I'm without a Haskell compiler, but shouldn't that be "exists a."?

The problem is that "exists" is not valid in either Haskell 98 or any current extension, whereas "forall" is a very common extension. But you can simulate "exists" via "forall", which is the thrust of these approaches.

brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [email protected]
system administrator [openafs,heimdal,too many hats] [email protected]
electrical and computer engineering, carnegie mellon university    KF8NH

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