When designing the full Kanren, we have experimented with two-continuation actions and various plumbing combinators (any, all, deterministic-all, etc). We eventually gave up on this after we realized that a simple interface suffices. Called MonadMinus, it is capable of defining LogicT monad with the true logical negation as well as interleaving and committed choice. Our ICFP05 paper describes MonadMinus monad (actually, the transformer) and LogicT as well as their two implementations. One of them uses success and failure continuations, and the other is based on delimited continuations. The latter offer an additional way to report `out-of-band' errors and continue parsing after the error has been `fixed'. http://okmij.org/ftp/Computation/monads.html#LogicT It is fair to say that whereas foldr/build and destroy/unfoldr fusion techniques work for Haskell lists, msplit/reflect in the LogicT paper is a fusion law for a general backtracking computation over arbitrary, perhaps even strict, base monad. That computation may look nothing like list; in fact, the LogicT paper gives an example with delimited continuations, with abort playing the role of nil and shift the role of cons.