module type HashedType : sig ... end
The input signature of the functor Hashtbl.Make.
t is the type of keys.
equal is the equality predicate used to compare keys.
hash is a hashing function on keys, returning a non-negative
integer. It must be such that if two keys are equal according
to equal, then they must have identical hash values as computed
by hash.
Examples: suitable (equal, hash) pairs for arbitrary key
types include
((=), Hashtbl.hash) for comparing objects by structure, and
((==), Hashtbl.hash) for comparing objects by addresses
(e.g. for mutable or cyclic keys).