11 Sep
2002
11 Sep
'02
5:36 p.m.
Manuel M T Chakravarty <chak@cse.unsw.edu.au> writes:
Sure, but there is also null = (== []) in the Prelude and `Maybe.isNothing'.
No, the definition of null is null [] = True which is quite different from (==[]) because it has a less-constrained type. null :: [a] -> Bool (==[]) :: Eq a => [a] -> Bool Likewise, isNothing :: Maybe a -> Bool (==Nothing) :: Eq a => Maybe a -> Bool So there are good reasons for having separate predicates testing the null/empty case at those polymorphic types, but no reason (except consistency of naming) for a pseudo-polymorphic type like Ptr a. However, consistency of naming is perhaps sufficient reason to add them anyway. Regards, Malcolm