The Generic Haskell user's guide, Version 1.60 - Diamond release

Abstract

Software development often consists of designing datatypes around which functionality is added. Some functionality is datatype specific, whereas other functionality is defined on almost all datatypes in a way that depends only on the structure of the datatype. A function that works on many datatypes in this manner is called a generic (or polytypic) function. Examples of generic functionality include editing, pretty-printing or storing a value in a database, and comparing two values for equality. Since datatypes often change and new datatypes are introduced, we have developed Generic H ASKELL, an extension of the functional programming language Haskell [11] that supports generic definitions, to save the programmer from (re)writing instances of generic functions. The original design of Generic H ASKELL is based on work by Ralf Hinze [3]. The current release is based on recent work by Dave Clarke, Johan Jeuring and Andres L¨oh [10, 9]. It extends Haskell with, among other things, a construct for defining type-indexed values. These values can be specialised to all Haskell datatypes, facilitating wider application of generic programming than provided by earlier systems such as PolyP [8].