Can You Really Reason Haskell Functions?

Philip Wadler is one of the founding fathers of Haskell and discovered a lot of really great stuff like that. Since Python has adopted, well, type hints they call, but basically allows you to have type signatures. It's just, it's, I mean, it helps dramatically in understanding the function or just even knowing, oh, well, this is a string that goes in and an input comes out. You can get things like that.