Abstract not found

Coding standards and good practices are important for all software projects, whatever programming languages they employ. Arguably, Prolog programming can benefit from a disciplined approach more than programming in other languages. Despite this, no widely accepted standards and practices seem to have emerged up to now. The present paper aims at being a first step towards filling this gap.

We discuss type classes in the context of the Chameleon language, a Haskell-style language where overloading resolution is expressed in terms of the meta-language of Constraint Handling Rules (CHRs). In a first step, we show how to encode Haskell’s single-parameter type classes into Chameleon. The encoding works by providing an approrpriate set of CHRs which mimic the Haskell conditions. We also consider constructor classes, multi-parameter type classes and functional dependencies. Chameleon provides a testbed to experiment with new overloading features. We show how some novel features such as universal quantification in context can naturally be expressed in Chameleon. 1.

Standard presentations of type class translation schemes exhibit some surprising problems when translating Haskell 98 programs. We suggests ways how to fix these problems based on a formal framework for extracting programs from type class proofs. Our description includes type improvement and recursive dictionaries – something which has not been formally studied before. Thus, we are able to advance the state of art of translating type classes and open up the possibility for new type class applications.