[newgame]

> His argument against Hindley-Milner seems to be that "he hates it", and that type errors are sometimes hard to understand. It is true IMO that they are hard to understand (even though, like everything in programming, you get better with practice), but what is the alternative? Debugging runtime errors while on production?

He pointed out that a more nominal type system is a solution. Because when you give meaningful names to your types the error messages will become clearer and not full of long, inferred types that reveal potentially confusing or unimportant implementation details.

[mafribe]

Most programming languages with Damas-Hindley-Milner do not prevent you from using explicit type annotation, and inventing semantically meaningful type names.

More importantly, I think the reason why error messages are sparse and not meaningful in languages with Damas-Hindley-Milner is that nobody bothered to improve the situation. And the reason why nobody botheres is that it's simply not a problem in practise. Any even moderately experienced programmer can easily detect and fix typing errors as they are given in Haskell, Ocaml, F#, Scala etc.