Mercury (relative of Prolog) greatly simplifies constraint solving and parsing as well. Packrat parsers for PEGs (a kind of unambiguous grammar) are a natural

Mercury (relative of Prolog) greatly simplifies constraint solving and parsing as well. Packrat parsers for PEGs (a kind of unambiguous grammar) are a natural consequence of Mercury's support for DCG notation and memoization. Mercury also has builtin support for user-defined constraint solvers.