Maintaining an equivalence relation implemented as union-find using STT
Description
This is an implementation of Tarjan's Union-Find algorithm (Robert E.
Tarjan. "Efficiency of a Good But Not Linear Set Union Algorithm", JACM 22(2),
1975) in order to maintain an equivalence relation. This implementation is a
port of the /union-find/ package using the ST monad transformer (instead of the
IO monad).
