On Tue, 10 Apr 2012 16:57:38 -0300 j.romildo@gmail.com wrote:
Hello.
Given the following function definitions
f 0 = True
g False = True
ghc infers the following types for the functions:
f :: (Eq a, Num a) => a -> Bool g :: Bool -> Bool
Why f has "Eq a" in the context in ts type, and g does not?
Bool is an instance of Eq, so there's no need to say that your
(non-existent) type variable has that constraint.
Using a numeric constants means you get a type variable with the Num
constraint. Since Num doesn't imply Eq, that constraint is (as Tim
pointed out) required so the guard can be checked.