Coalton brings Haskell-style static typing to Common Lisp

Coalton is a statically typed functional language that runs on top of Common Lisp, blending Lisp’s macro-driven flexibility with type system ideas borrowed from Haskell, Scheme, and OCaml. The project positions itself as a way to write efficient, type-safe code without abandoning the Common Lisp ecosystem.

The site highlights a May 2025 ELS talk by Robert Smith covering the language’s design and direction. For Lisp developers who have long admired ML-family type systems but didn’t want to leave the REPL-driven workflow behind, Coalton offers a middle path: parametric polymorphism and type classes layered onto a host language known for dynamic introspection.