Module type `Hashcons.HashconsedType`

Generic hashconsing signature

Given an equivalence relation eq, a hashconsing function is a function that associates the same canonical element to two elements related by eq. Usually, the element chosen is canonical w.r.t. physical equality (==), so as to reduce memory consumption and enhance efficiency of equality tests.

In order to ensure canonicality, we need a way to remember the element associated to a class of equivalence; this is done using the table type generated by the Make functor.

type t: Type of objects to hashcons.

type u: Type of hashcons functions for the sub-structures contained in t. Usually a tuple of functions.

val hashcons : u -> t -> t: The actual hashconsing function, using its fist argument to recursively hashcons substructures. It should be compatible with eq, that is eq x (hashcons f x) = true.

val eq : t -> t -> bool: A comparison function. It is allowed to use physical equality on the sub-terms hashconsed by the hashcons function, but it should be insensible to shallow copy of the compared object.

val hash : t -> int: A hash function passed to the underlying hashtable structure. hash should be compatible with eq, i.e. if eq x y = true then hash x = hash y.