Polytypic Programming in Haskell

Ulf Norell and Patrik Jansson

Paper presented at IFL'03, in press for LNCS, 2004.

Full paper: .ps.gz and implementation


A polytypic (or generic) program captures a common pattern of computation over different datatypes by abstracting over the structure of the datatype. Examples of algorithms that can be defined polytypically are equality tests, mapping functions and pretty printers.

A commonly used technique to implement polytypic programming is specialization, where a specialized version of a polytypic function is generated for every datatype it is used at. In this paper we describe an alternative technique that allows polytypic functions to be defined using Haskell's class system (extended with multi-parameter type classes and functional dependencies). This technique brings the power of polytypic programming inside Haskell allowing us to define a Haskell library of polytypic functions. It also increases our flexibility, reducing the dependency on a polytypic language compiler.

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Patrik Jansson / NOpatrikjSP@AMchalmers.se