Though exponential in complexity, type inference in Hindley-Milner is always fast for programs of human interest. The type system is rich enough to allow the expression of complex structural invariants. It is so rich, in fact, that well-typed programs are often bug-free. Recommended reading ML...
1.6.2 Compliance with Automata TheoryIn previous versions of Spin the synchronous product of the system state space with the Büchi automaton that corresponds to a never claim was defined such that no proposition could be checked on the initial system state (the root of the reachability tree). ...