In this paper we describe progress towards a theory of tranformational program development. The transformation rules are based on a theory of contextual equivalence for functional languages with imperative features. Such notions of equivalence are fundamental for the process of program specification, derivation, transformation, refinement and other forms of code generation and optimization. This paper is dedicated to Professor Satoru Takasu.
Keywords: functional, imperative, ML, Scheme, program equivalence, program transformation, contextual assertion, VTLoE