We introduce a constraint-based framework for strictness analysis
applicable to ML style languages supporting higher-order functions,
let-style polymorphism and algebraic datatypes. The analysis
produces strictness types for expressions in a program. A
strictness type is defined using Boolean constraints.
Perhaps surprisingly, the Boolean constraints that arise during
analysis are in HORN, which makes the operations on them amenable to
efficient implementation.
We have implemented the approach within a highly optimising Haskell
compiler (GHC) and give a comparison with the current strictness
analyser of GHC.
