Formal development of correct algorithms: An example based on Earley's recogniser

Abstract

This paper contains the formal development of a correct algorithm from an implicit definition of the task to be performed. Each step of the development can be accompanied by a proof of its correctness. As well as ensuring the correctness of the final program, the structured development gives considerable insight into the algorithm and possible alternatives. The example used is a simplified form of the recognition algorithm due to Earley.