A Concurrent Constraint Handling Rules Implementation in Haskell With Software Transactional Memory

Constraint Handling Rules (CHR) is a concurrent committed choice constraint logic programming language to describe transformations (rewritings) among multi-sets of constraints (atomic formulae). CHR is widely used in a range of applications spanning from type system design to artificial intelligence. However, none of the existing CHR implementations the authors are aware of exploits concurrency or parallelism explicitly. They give a concurrent CHR implementation using GHC (Glasgow Haskell Compiler) with support for Software Transactional Memory. They achieve some significant performance improvements compared to a single-threaded CHR implementation.