Dependent types provide an unprecedented level of type safety. A quick example is a type-safe printf implementation. They are also useful for theorem proving. According to the Curry-Howard correspondence, mathematical propositions can be represented in a program as types. An implementation that satisfies a given type serves as a proof of the corresponding proposition. In other words, inhabited types represent true propositions.

I have a long-standing desire for a JavaScript library that provides good implementations of functional data structures. Recently I found Mori, and I think that it may be just the library that I have been looking for. Mori packages data structures from the Clojure standard library for use in JavaScript code. …