Many useful programming constructions can be expressed as
monads. Examples include probabilistic modeling, functional reactive
programming, parsing, and information flow tracking, not to mention
effectful functionality like state and I/O. We present a type-based
rewriting algorithm to make programming with arbitrary monads as easy
as using ML's built-in support for state and I/O. Developers write
programs using monadic values of type m τ as if they were of type τ,
and our algorithm inserts the necessary binds, units, and
monad-to-monad morphisms so that the program type checks.
Coco is a prototype implementation of our approach for core ML. We
will demonstrate how to take advantage of Coco to facilitate using
monadic libraries in practice.