It also has a much more powerful, but also more complex type system. To be precise, it's type _inference_ of Damas-Hindley-Milner + Typeclasses that poses the

It also has a much more powerful, but also more complex type system. To be precise, it's type _inference_ of Damas-Hindley-Milner + Typeclasses that poses the most gotchas. (Plain vanilla DHM is just ML. You can hack Haskell without class, but you can't get the class out of Haskell.) Experience with Prolog helps, since a form of logical deduction, generally speaking, is what's happening behind the scenes. You could think of the compiler as applying AI to figure out the types. This kind of AI is magic when it works and baffling when it barfs. One way out is to skip the AI entirely and annotate all the types by hand. Now the compiler only has to check types, not infer them. When it stumbles over imperfect code, the error messages become a lot more decipherable.