The HERMIT in the Tree

Abstract

Abstract. This paper describes our experience using the HERMIT toolkit to apply well-known transformations to the internal core language of the Glasgow Haskell Compiler. HERMIT provides several mechanisms to support writing general-purpose transformations: a domain-specific language for strategic programming specialized to GHC's core language, a library of primitive rewrites, and a shell-style-based scripting language for interactive and batch usage. There are many program transformation techniques that have been described in the literature but have not been mechanized and made available inside GHC -either because they are too specialized to include in a general-purpose compiler, or because the developers' interest is in theory rather than implementation. The mechanization process can often reveal pragmatic obstacles that are glossed over in pen-and-paper proofs; understanding and removing these obstacles is our concern. Using HERMIT, we implement eleven examples of three program transformations, report on our experience, and describe improvements made in the process.

Space Improvements and Equivalences in a Functional Core Language

“…We discuss some previous work on time and space behavior for call-by-need functional languages. Examples of research on the correctness of program transformations are in [13,9,20], examples of the use of transformations in optimization in functional languages are in [14,21]. A theory of (time) optimizations of call-by-need functional languages was started in [11] for a call-by-need higher order language, also based on a variant of Sestoft's abstract machine [22].…”