It is a continuation-based, backtracking, logic programming monad. an adaptation of the two-continuation implementation found in the paper backtracking, interleaving, and terminating monad transformers available here: http://okmij.org/ftp/papers/logict.pdf

this package provides a library for the haskell programming language, compiled for profiling. see http://www.haskell.org/ for more information on haskell.