Meta-Programming with Tabaluga

We present a lightweight approach to meta-programming in the functional programming language Haskell. In this approach, meta-programs are constructed with the help of generalised (possibly monadic) folds over the system of datatypes that represents the abstract syntax of the objectlanguage. Such folds are obtained by (1) reusing, refining, and combining basic fold algebras, and (2) feeding the resulting fold algebra to a fold function. A library of basic fold algebras, combinators and fold functions can be generated from a system of datatypes by our tool Tabaluga. To demonstrate this technique of meta-programming with folds, we present a case study involving Haskell itself as object-language: a simple application extractor, which analyses and transforms collections of Haskell modules to remove unused (library) code.