Make.1-XGiven 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.
The actual hashconsing function. It should be compatible with eq, that is eq x (snd @@ hashcons f x) = true. It also returns the hash.
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. It should be compatible with the hash returned by hashcons, ie eq x y implies fst @@ hashcons x = fst @@ hashcons y.