Re: [Haskell-cafe] 'data' syntax - a suggestion

On 9/27/07, jerzy.karczmarczuk@info.unicaen.fr wrote:

Thomas Conway writes:

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On 9/27/07, ok wrote:

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I have often found myself wishing for a small extension to the syntax of Haskell 'data' declarations. It goes like this: ['where' clause to allow locally defined names in type declarations]

Nice.

Quite a few times I've found myself declaring type synonyms for this reason, but you end up polluting the global namespace.

+1 vote.

Data with where? You haven't heard about GADTs?

I think that you haven't read the question carefully, because "where" in GADTs is simply a syntactic sugar. However, this seems to be available already with GADTs and type equality constraints: data BST key val where Empty :: BST key val Fork :: (bst ~ BST key val) => key -> val -> bst -> bst -> BST key val It's a pity you can't use bst (or a type synonym) instead of the last "BST key val". Best regards Tomasz