[Haskell-cafe] Context for type parameters of type constructors

Keith Wansbrough Keith.Wansbrough at cl.cam.ac.uk
Tue Mar 30 13:05:55 EST 2004

> My question was why he doesn't believe that. My definition
>   data (Num a) => VList a = VList [a]
>  clearly states that VLists will ever get types of class Num as
> parameters. 

Ah.  Constraints on datatype declarations are a misfeature of Haskell, and 
have no useful effect.  You shouldn't use them.

--KW 8-)
Keith Wansbrough <kw217 at cl.cam.ac.uk>
University of Cambridge Computer Laboratory.

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