Fix offers support for computing the least solution of a set of monotone equations, as described in the unpublished paper "Lazy Least Fixed Points in ML". In other words, it allows defining a recursive function of type variable -> property, where cyclic dependencies between variables are allowed, and properties must be equipped with a partial order. The function thus obtained performs the fixed point computation on demand, in an incremental manner, and is memoizing.
Make constructs a solver for a type key that is equipped with an implementation of imperative maps and a type property that is equipped with bottom, equal, and is_maximal functions.
ForOrderedType is a special case of Make where it suffices to pass an ordered type T as an argument. A reference to a persistent map is used to hold the memoization table.
module ForOrderedType (T : Map.OrderedType) (P : sig ... end) : sig ... endForHashedType is a special case of Make where it suffices to pass a hashed type T as an argument. A hash table is used to hold the memoization table.
module ForHashedType (T : Hashtbl.HashedType) (P : sig ... end) : sig ... endForType is a special case of Make where it suffices to pass an arbitrary type T as an argument. A hash table is used to hold the memoization table. OCaml's built-in generic equality and hash functions are used.