Transforming Haskell for Tracing

Hat is a programmer’s tool for generating a trace of a computation

of a Haskell 98 program and viewing such a trace in various

different ways. Applications include program comprehension and debugging.

A new version of Hat uses a stand-alone program transformation to

produce self-tracing Haskell programs. The transformation is small and

works with any Haskell 98 compiler that implements the standard foreign

function interface. We present general techniques for building compiler

independent tools similar to Hat based on program transformation. We

also point out which features of Haskell 98 caused us particular grief.