A Type Inferencer for ML in 200 Lines of Scala
summary
Shows a working implementation of Wand's algorithm for a tiny Standard ML subset implemented in 200 lines of Scala, with the compiler split into type annotation + constraint generation + unification. The code generates type placeholders, emits set-based constraints, and solves them by unification to recover ML-style polymorphism; it handles ordinary ML programs but fails on higher-rank polymorphism (undecidable cases) and some construct combinations that require more than simple unification. Code and slides are available.
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