[Haskell-beginners] Various style at instance of a typeclass
stephen.tetley at gmail.com
Wed Jun 29 16:21:37 CEST 2011
The class Monad is more specifically a "constructor class" rather than
a type class.
Constructor classes have particular arities (numbers of parameters -
"holes") called "kinds".
Monad is a constructor class with kind :: * -> *
(Write w) - has kind :: * -> *
Write - has kind :: * -> * -> *
(Write w a) - has kind :: *
Thus only the first is compatible with the Monad class.
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