Magma2
A language that allows programmability of the control environment, e.g. recursion, backtracking, coroutines, nondeterminism, etc. Magma2 was the successor to MagmaLISP.
["Magma2: A Language Oriented Toward Experiments in Control", Franco Turini, ACM TOPLAS 6(4):468-486 (Oct 1984)].