From what I have heard, they are completely subsumed by GADTs, which is a stable enough extension that it was considered unimportant to save. Your Foo would be something like this: data Foo a where Foo :: Eq a => a -> Foo a On 4/25/2013 6:38 AM, harry wrote:
If I understand correctly, the problem with datatype contexts is that if we have e.g. data Eq a => Foo a = Foo a the constraint Eq a is thrown away after a Foo is constructed, and any method using Foos must repeat Eq a in its type signature.
Why were these contexts removed from the language, instead of "fixing" them?
PS This is following up on a discussion on haskell-beginners, "How to avoid repeating a type restriction from a data constructor". I'm interested in knowing whether there's a good reason not to allow this, or if it's just a consequence of the way type classes are implemented by compilers.
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