> number of hacks These are not hacks, subtyping and GADT are part of the core language > ML's type system is much less powerful than Haskell's or Scala's Ye

> number of hacks These are not hacks, subtyping and GADT are part of the core language > ML's type system is much less powerful than Haskell's or Scala's Yes, but most of the fancy stuff is located in the module language, and it doesn't lack power, it lacks implicitness (until modular implicits would land).