Extensible record

Proposals, implementations can be found on the FirstClassLabels page of Haskell' Wiki.

Papers and libraries

• HList – a Haskell library for strongly typed heterogeneous collections includes also extensible records. Its relatedness to database programming is described in the articles, see also its possible relatedness to HaskellDB project.
• Daan Leijen: First-class labels for extensible rows. See also the description of the Haskell-like language Morrow, it is based on the concepts of the article. And Extensible records with scoped labels: "We describe a natural approach to typing polymorphic and extensible records that is simple, easy to use in practice, and straightforward to implement."
• Simon Peyton Jones and Greg Morrisett: A proposal for records in Haskell
• Mark Jones and Simon Peyton Jones: Lightweight Extensible Records for Haskell
• Mark P. Jones: A prototype implementation of extensible records for Hugs
• Didier Remy's Typing record concatenation for free on Erik Knoop's page
• Benedict R. Gaster, Mark P. Jones: A Polymorphic Type System for Extensible Records and Variants
• Chameleon, a Haskell-like language, see its records [dead link as of 2011-09-15]
• Grapefruit contains the package grapefruit-records which implements a record system in Haskell with GHC extensions. This record system allows field selection and dropping of fields using pattern matching. It also supports defaulting.
• Generic Record Combinators with Static Type Checking describes a record system with several novel features, which is provided by the records package. It is derived from the record system of Grapefruit.
• The extensible-data package includes extensible records.

Applications

Declarative database management

Such systems can achieve more type safety (compared to direct SQL handling). They usually formulate a relational algebra concept in a declarative language.

HaskellDB

A problem where some concepts of extensible records could be useful is described in the HaskellDB project. More precisely, the problem is described in the paper downloadable from

• Chalmers version of HaskellDB (see Papers subsection on Documentation)
• which presupposes reading also paper on the Daan Leijen's original HaskellDB page (see Documentation subpage, PostScript version)

HaskellDB uses its own extensible record system, but see also HaskellDB#Future.

CoddFish

CoddFish is another declarative, type safe database system. As for extensible record system, it uses HList --- a Haskell library for strongly typed heterogeneous collections.

Functional Reactive Programming

FRP often makes it necessary to deal with very large tuples as arrow inputs and outputs. For example, a GUI component would receive the behavior of all its writeable properties as its input. Extensible records can therefore make FRP more usable, especially if they provide defaulting.

Grapefruit

Grapefruit uses extensible records which support pattern matching and defaulting for functional reactive GUI programming.

Related concepts

Dependent type -- as an explanation for its relatedness here, see Why Dependent Types Matter written by Thorsten Altenkirch, Conor McBride, James McKinna -- or see at least its Conclusions section (section 8, pages 18--19).

Type arithmetic seems to me also a way yielding some tastes from dependent type theory.

Relational algebra implementations usually use extensible records.