Functional low-level interpreters

We show how to construct in a pure, lazy functional language Haskell a low-level, FORTH-like (stack based, postfix style) virtual machine, used as a target platform in our compilation course for computer science students. The implementation is clear, reasonably efficient, and easily extensible. Two models are presented: more “classical”, with a separate return stack, and an interpreter based on the continuation-passing style. The idea, although traditional, was a bit experimental, since this was the first contact of our students with Haskell and with advanced functional techniques. We exploited thus this course to teach also those techniques, on a comprehensive and conceptually coherent set of examples.