module type HashedType =sig..end
The input signature of the functor MoreLabels.Hashtbl.Make.
type 
The type of the hashtable keys.
val equal : t -> t -> boolThe equality predicate used to compare keys.
val hash : t -> intA hashing function on keys. It must be such that if two keys are
            equal according to equal, then they have identical hash values
            as computed by hash.
            Examples: suitable (equal, hash) pairs for arbitrary key
            types include
(=), MoreLabels.Hashtbl.HashedType.hash) for comparing objects by structure
                (provided objects do not contain floats)(fun x y -> compare x y = 0), MoreLabels.Hashtbl.HashedType.hash)
                for comparing objects by structure
                and handling nan correctly(==), MoreLabels.Hashtbl.HashedType.hash) for comparing objects by physical
                equality (e.g. for mutable or cyclic objects).