Lambda the Ultimate

A Debugging Environment for Lazy Functional Languages

Abstract: This paper describes a new approach for debugging lazy functional languages. It rests on the fact that a functional program is the transformation of an expression; one debugs a program by investigating the syntactic form of the expression and by stopping the reduction process at given points. We show what problems are involved and our approach to solving them in a prototype implementation.

I remember there was a discussion of difficulties with lazy FPL debugging, and I didn't find a reference to this paper on LtU, so...

PS: beware, "a new approach" means around 96-99 :)