I'm not sure I'd say this is "the other way around"; Coalton strives to implement Haskell or ML-adjacent semantics (in the type system, for example) with Lisp syntax. "With" here meaning that it is both implemented in and written with Lisp syntax.

Edit: I think I see what you mean now. Lisp backend vs Haskell backend.

Anyway, Coalton is a joy to use and IMO a breath of fresh air in CL. It's quite easy start using as a library; go all-in or only use it in specific parts of the code. It's great to be able to choose between (or intermix)the flexibility of CL and the guarantees of a statically typed language (as well as some nice performance boosts with arguably less work). Some aspects are still young (some of the standard library, ecosystem, editor support), but it's quite thoughtfully crafted and I'm excited to see where it goes.