Project Oscar
Loïc CORRENSON, Etienne DURIS,
Didier PARIGOT and Gilles ROUSSEL
The deforestation of a functional program is a transformation which gets rid of intermediate data structures constructions that appear when two functions are composed. The descriptional composition, initially introduced by Ganzinger and Giegerich, is a deforestation method dedicated to the composition of two attribute grammars. This article presents a new functional deforestation technique, called symbolic composition, based on the descriptional composition mechanism, but extending it. An automatic translation from a functional program into an equivalent attribute grammar allows symbolic composition to be applied, and then the result can be translated back into a functional program. This yields a source to source functional program transformation. The resulting deforestation method provides a better deforestation than other existing functional techniques. Symbolic composition, that uses the declarative and descriptional features of attribute grammars is intrinsically more powerful than categorical-flavored transformations, whose recursion schemes are set by functors. These results tend to show that attribute grammars are a simple intermediate representation, particularly well-suited for program transformations.
Keywords: Deforestation, attribute grammars, functional programming, program transformation, partial evaluation.