From Haskell to a New Structured Combinator Processor

This paper presents KappaMutor, a new graph reduction processor, along with its Haskell compiler. KappaMutor is based on structured combinators, a recently proposed combinator encoding, which is more flexible and efficient than fine-grained SKI combinators. The processor exploits parallel memories to enable single-cycle reduction of structured combinators while maintaining good compactness, utilising less than 1% of the logical resources on a modern FPGA. Its Haskell compiler implements novel code generation strategies designed to minimise combinator usage and achieve full laziness --- the first such implementation for structured combinators, to the best of our knowledge. Based on our measurements, structured combinators can reduce runtimes by 9% to 58%, compared to running equivalent SKI combinator programs on KappaMutor.