Screamer is an extension of Common Lisp that adds support for nondeterministic programming.
Screamer consists of two levels.
The basic nondeterministic level adds support for backtracking and undoable side effects. On top of this nondeterministic substrate, Screamer provides a comprehensive constraint programming language in which one can formulate and solve mixed systems of numeric and symbolic constraints. Furthermore, Screamer is fully integrated with Common Lisp. Screamer programs can coexist and interoperate with other extensions to Common Lisp such as CLOS, CLIM and Iterate. In several ways Screamer is more efficient than other implementations of backtracking languages.