Type classes

[jparoz]

Implement type classes, similar to those found in Haskell and other languages.

These could be implemented as a new type of Constraint, and integrated into the existing constraint solver; or possibly something more similar to ExplicitTypeConstraint with a separate constraint queue, if the solving doesn't need to be interleaved with the existing type inference constraints.

• Do notation
  • Is this notation tied to a Monad typeclass, or Applicative, or some other more abstract thing (e.g. it uses whichever >>= and >> operators that are in scope)? Needs more investigation

Interesting paper from SPJ: Tackling the Awkward Squad: monadic input/output, concurrency, exceptions, and foreign-language calls in Haskell