[Haskell-cafe] Adding Ord constraint to instance Monad Set?
MR K P SCHUPKE
k.schupke at imperial.ac.uk
Wed Mar 31 13:03:37 EST 2004
But that is already used for existential datatypes:
data Test = forall a . Num a => Test a
Maybe that lack of forall is enough to distinguish the two though. Your
example would currently be written:
data (Ord a,Num b) => Either a b = Left a | Right b
I dont have any problem with this, just remember these are constraints
on function arguments... It my superficially look like a class system,
but in reality it is more like a constraint based programming language
(for example Prolog) at the type level...
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