Hask
Categories: Stub articles | Mathematics | Theoretical foundations
Hask is the name usually given to the category having Haskell types as objects and Haskell functions between them as morphisms.
A type-constructor that is an instance of the Functor class is an endofunctor on Hask.
A solution approach to the issue of partiality making many of the identities required by categorical constructions not literally true in Haskell:
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The seq problem
The right identity law fails in Hask if we distinguish values which can be distinguished by seq, since:
id . undefined = \x -> id (undefined x) = \x -> undefined x
should be equal to undefined, but can be distinguished from it using seq:
ghci>(undefined :: Int -> Int) `seq` ()* Exception: Prelude.undefined ghci>(id . undefined :: Int -> Int) `seq` ()()
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