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
(=), hash) for comparing objects by structure (provided objects do not contain floats)(fun x y -> compare x y = 0), hash) for comparing objects by structure and handling Stdlib.nan correctly(==), hash) for comparing objects by physical equality (e.g. for mutable or cyclic objects).