algo_w - Algorithm W extended with "Extensible Records with Scoped Labels" and Multi Parameter Typeclasses.

This follows closely tomprimozic/type-systems and then THIH (Typing Haskell in Haskell). Note that this tries to support multi-parameter typeclasses (MPTC) but generalization is currently buggy for typeclasses with multiple parameters. See hmx_tc implementation for the bug-free HM + MPTC implementation.

hmx - HM(X) style implementation of Hindley Minler type inference.

The main idea is to introduce constraint language and split the algo into two phases — first generate constraints from terms, then solve those constraints.

This implementation also does elaboration, the infer function has the following signature:

val infer : env:Env.t -> expr -> (expr, Error.t) result

That means that infer returns not just the type of the expression but an elaborated expression (an original expression annotated with types).

The elaboration mechanism is shamelessly stolen from inferno.

hmx_tc - extends HM(X) with Multi-Parameter Typeclasses (MPTC).

Type inference and elaborator are implemented but the environment construction doesn't check for overlapping instances yet.