Testing and Tracing Lazy Functional Programs using QuickCheck and Hat

It is a very undesirable situation that today’s software often contains errors. One motivation for using a functional programming language is that it is more difficult (or even impossible) to make low-level mistakes, and it is easier to reason about programs. But even the most advanced functional programmers are not infallible; they misunderstand the properties of their own programs, or those of others, and so commit errors