Bol Processor grammars are an extension of unrestricted generative grammars allowing a simple representation of string "patterns", here taken to mean repetitions and homomorphic transformations. These have been successfully applied to the simulation of improvisatory techniques in traditional drum music, using a production-rule system called "Bol Processor BP1". The basic concepts and parsing techniques of BP1 are presented.

A new version of Bol Processor, namely "BP2", has been designed to serve as a aid to rule-based composition in contemporary music. Extensions of the syntactic model, such as metavariables, remote contexts, substitutions and programmed grammars, are briefly introduced.