Try :t (foo 2, moo 2) On 3 Aug 2011, at 23:31, Patrick Browne wrote:
Below are examples of using the sub-class context at class level and at instance level. In this simple case they seem to give the same results In general, are there certain situations in which one or the other is preferred? Pat module CLASS where -- class and sub-class class Class a where foo :: a -> a foo a = a class Class a => SubClass a where moo :: a -> a moo a = foo a instance Class Integer where instance SubClass Integer where *CLASS> :t foo 2 foo 2 :: forall t. (Class t, Num t) => t *CLASS> :t moo 2 moo 2 :: forall t. (SubClass t, Num t) => t module INSTANCE where -- Using context at instance level -- Is class Class a where foo :: a -> a foo a = a class SubClass a where moo :: a -> a
instance Class Integer where instance Class Integer => SubClass Integer where moo a = foo a INSTANCE> :t foo 2 foo 2 :: forall t. (Class t, Num t) => t INSTANCE> :t moo 2 moo 2 :: forall t. (SubClass t, Num t) => t _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe