Making “stricterness” more relevant

Adapting a strictness analyser to have it take into account explicit strictness annotations can be a tricky business. Straightforward extensions of analyses based on relevance typing are likely to either be unsafe or fail to pick the fruits of increases in strictness that are introduced through annotations. We propose a more involved adaptation of relevance typing, that can be used to derive strictness analyses that are both safe and effective in the presence of explicit strictness annotations. The resulting type system provides a firm foundation for implementations of type-based strictness analysers in compilers for lazy programming languages such as Haskell and Clean.