Hi all, an explicit given signature causes ghc to choose the right types for integer literals as in {-# OPTIONS -fglasgow-exts #-} import Data.Map f :: Ord a => [a] -> Map a Int f xs = fromList $ zip xs [0..] Here the Literal 0 is threated as (0::Int). But the setting {-# OPTIONS -fglasgow-exts #-} import Data.Map class New a b where new :: a -> b instance Ord a => New [(a,b)] (Map a b) where new = fromList g :: Ord a => [a] -> Map a Int g xs = new $ zip xs [0..] causes the error message Could not deduce (New [(a, b)] (Map a Int)) from the context (Ord a) arising from use of `new' at Why.hs:10:7-9 ghc seems to be unable to threat the Literal 0 as (0::Int) this time but I do not understand why :-( Can anyone explain it? Thanks, -- -- Mirko Rahn -- Tel +49-721 608 7504 -- --- http://liinwww.ira.uka.de/~rahn/ ---