This is (currently only one) example for the usage of matchable library.
In Unification, it implements an unification algorithm
generically using the Matchable type class and the Free monad.
In MiniProlog, it implements very tiny logic programming DSL,
inspired by Prolog, using Unification module. The point is Unification module is
not tailored only for MiniProlog's usage.
In Main, it shows MiniProlog is working by examples.