Mathieu will be using CHRs (Constraint Handling Rules) as the basic underlying technology for type checking in Yhc/nhc98. The approach is already used by Sulzmann's Chameleon system, and Leijen's MLF.

Stage 1: write a CHR engine.

Stage 2: steal constraint rules for Haskell type-inference from Chameleon.

Stage 3: add new CHRs to handle Haskell type system extensions.

As of 20th August, we have a type-checking library called TaiChi, which achieves stages 1 & 2. During Sept, we hope to add stage 3.