th-deepstrict: Enforcing deep strictness properties using Template Haskell

Excessive laziness is a common worry when analyzing the performance characteristics of Haskell programs. It can lead to higher than expected memory usage due to heap objects being retained for longer than necessary. This is known as a “space leak”. Like any other performance issue, it can be tricky to track down and fix, especially in large, complex codebases.

At Tracis we have written a library, th-deepstrict, to help avoid this class of problem by asserting the strictness of a datatype at compile time.

We will give a brief introduction to excessive laziness; survey existing tools; and then present th-deepstrict.