[nytopop]

Check out the hindley milner type system [1]. It's used by haskell and some other languages, and allows for a very extensive amount of type inference. You can often write large sections of code with no type annotations and the compiler can figure out the most general type based on the type of some function called somewhere, which means the thing you did with that result must be of a certain class of types, which makes the surrounding expressions' types have to be a certain class of types, etc etc.

[1] https://en.wikipedia.org/wiki/Hindley%E2%80%93Milner_type_sy...

[cwzwarich]

I think it's fair to say that (GHC) Haskell no longer really uses the Hindley-Milner type system. It doesn't have let generalization (except in a few restricted cases), and it doesn't have principal types, which I would consider to be the two distinguishing features of HM.

[danharaj]

Let generalization should only be disabled if one uses the GADT type extension and even then can be turned on in addition to GADTs. While Haskell isn't really Hindley-Milner, it's close enough for most development.