TIM: A simple, lazy abstract machine to execute supercombinatorics

This paper is a description of the three instruction machine Tim, an abstract machine for the execution of supercombinators. Tim usually executes programmes faster than the G-machine style of abstract machine while being at least as easy to implement as an S-K combinator reducer. It has a lower overhead for passing unevaluated arguments than the G-machine, resulting in good performance even without strictness analysis, and is probably easier to implement in hardware. The description begins with a presentation of the instruction set of the machine, followed by the operational semantics of the normal order version and the algorithm to convert combinators to instructions. It then develops the machine to allow lazy evaluation and the use of sharing and strictness analysis. The final sections of the paper give some performance figures and comment upon the suitability of the machine for hardware implementation.