module type HashedType =sig..end
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
((=), Hashtbl.hash) for comparing objects by structure,
((fun x y -> compare x y = 0), Hashtbl.hash)
for comparing objects by structure and handling Pervasives.nan
correctly, and
((==), Hashtbl.hash) for comparing objects by addresses
(e.g. for cyclic keys).