On 5/31/05, Daniel Fischer
Why is ghc unable the determine the type of the Literal 0 in the definition of g?
Answer: Since somewhere an instance e.g. New [(a,Double)] (Map a Int) could be defined, leading to problems when threating 0 as (0::Int).
There could be such an instance, but that's obviously not the case. At the point where g is defined, GHC only knows about New [(a,b)] (Map a b), and New [(a,Double)] (Map a Int) doesn't fit. Consider this: *Main> :type new . flip zip [0..] new . flip zip [0..] :: (New [(a, b1)] b, Num b1, Enum b1) => [a] -> b Trying to infer New [(u, v)] w out of all that we know, i.e. New [(a,b)] (Map a b) should give us w === Map u v ---> New [(u, v)] (Map u v) so finally v === Int ---> New [(u, Int)] (Map u Int) to infer the context of g. Is there any good reason not to do this? Cheers, D. Tenev