Constraints to Stop Deforestation

Wadler's deforestation algorithm eliminates intermediate data structures from functional programs. To be suitable for inclusion in a compiler, deforestation must terminate on all programs. Several techniques exist to ensure termination of deforestation on all rst-order programs, but general techniques for higher-order programs were introduced only recently by rst Hamilton and then Marlow. We present a new technique for ensuring termination of deforestation on all higher-order programs that allows useful transformation steps prohibited in Hamilton's and Marlow's techniques. The technique uses a constraint-based higher-order control-ow analysis. We also relate our technique to previous approaches to termination of rst-and higher-order deforestation in some detail.