Why is this function type-correct

Hello, Recently, I wrote a function similar to x :: a x = x 42 which is type-correct (Hugs, Ghc, THIH). Still, from the expression it is clear that the type shoud have a function type. The definition x :: a -> b x = x 42 is equally well accepted, though I can't see why this type would be correct. (I'd expect it to be too general.) For what reasons are these types considered correct? Thanks, Rijk-Jan