this paper, we propose an algorithm which can automatically turn all practical recursive definitions into structural hylomorphisms making program fusion be easily applied. 1 Introduction

Program fusion (or deforestation) is a well-known transformation whereby compositions of several pieces of code are fused into a single one, resulting in an efficient functional program without intermediate data structures. Recent work has made it clear that fusion transformation is especially successful if recursions are expressed in terms of hylomorphisms . The point of this success is that fusion transformation proceeds merely based on a simple but effective rule called Acid Rain Theorem [10]. However, there remains a problem. The Acid Rain Theorem can only handle hylomorphisms inducting over a single data structure. For hylomorphisms, like zip, which induct over multiple data structures, it will leave some of the data structures remained which should be removed. In this paper, we extend the Acid Rain Theorem so that it can deal with such hylomorphisms, enabling more intermediate data structures to be eliminated. 1. Introduction Functional programming constructs a complex program ...