On Thu, 12 Mar 1998, Koen Claessen wrote:
> Sadly, this example shows that Haskell 1.4 does not have a principal
> typing property. Your function has the type
>
> all' :: Eq a => (a -> Bool) -> [a] -> Bool
>
> As well as:
>
> all' :: Eq a => (a -> Bool) -> F a -> Bool
>
> (for a suitable Monad F). But Haskell is not capable of finding the one
> type that contains them all:
>
> all' :: (Monad m, Eq (m a)) => (a -> Bool) -> m a -> Bool
What is the reason for that? It is a language design choice or is there a
fundamental reason like, say, that allowing such things make the type
system undecidable?
m
-----------------------------------------------------------------------
Mariano Suarez Alvarez The introduction of
Departamento de Matematica numbers as coordinates
Universidad Nacional de Rosario [...] is an act of violence
Pellegrini 250 A. Weyl
2000 Rosario - Argentina
e-mail: [EMAIL PROTECTED]
-----------------------------------------------------------------------
