Applications and libraries

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The first place to look for data types or functions that do what you want is the Standard Prelude, then the Language and library specification (both parts of the Haskell standards documentation), then in whatever extra libraries are provided by the Haskell implementation you are using, then on the page you are looking at. If it is not here, then it may be in the archives of the Haskell Weekly News.

Search the standard libraries collection (by name or type signature) using Hoogle.

There is an effort underway to standardise many of the extra libraries that come with Haskell implementations, and at the same time extend the module namespace into a hierarchy. A document describing this project can be found here, and there is a mailing list for discussing issues related to libraries.

A large collection of standard hierarchical libraries are currently distributed with GHC (from version 5.04), Hugs (from Nov 2003), and nhc98 (from 1.16).

Cabal, The Common Architecture for Building Applications and Libraries, is an framework for packaging, building, and installing any tool developed in the Haskell language.

This page is intended as a comprehensive list of all Haskell libraries and tools. Some of these are proof-of-concepts rather than production code. Some have no longer been maintained for a long time.

On there is an alternative list of public domain software written in Haskell. That list is currently short (for you to change that), but in particular it displays the current development status of the software. Even more Haskell projects are documented in the community reports and in the archives of the Haskell Weekly News.

Program Development

Vital is a visual programming environment. It is particularly intended for supporting the open-ended, incremental style of development often preferred by end users (engineers, scientists, analysts, etc.).
hmake, a Haskell-aware replacement for make
Automatically keeps track of module dependencies (i.e. no need to write any Makefiles!). Can be used with any of the usual Haskell compilers (ghc, hbc, nhc98).
Cpphs is a re-implementation (in Haskell) of the C pre-processor.
DrIFT is a tool which allows derivation of instances for classes that aren't supported by the standard compilers. In addition, instances can be produced in seperate modules to that containing the type declaration. This allows instances to be derived for a type after the original module has been compiled. As a bonus, simple utility functions can also be produced from a type.
Hasktags is a simple program that generates TAGS files for Haskell code. Together with a supporting editor (e.g. NEdit, XEmacs, or Vim) TAGS files can be used to quickly find the places where functions, data constructors etc. are defined.
A version of the tags program for Haskell. It uses the standardised hssource and posix library, works with GHC 5.02.1. tags file has been checked to work with vim and nedit.
HaSpell is a spelling and style checker for Haskell programs. It can detect spelling errors in comments in the program text, and optionally in the code itself. There is an option to detect metasyntactic variables (such as 'foo') and 'bad function prefixes' such as 'compute' and 'doThe' - these make the program less readable and generally indicate bad programming style.
Uniform Workbench
This tool is an Integration Framework providing its services in the lazy functional programming language Haskell. The WorkBench provides support for data, control and presentation integration, so that integrated Software Development Environments can be constructed from the basis of prefabricated, off-the-shelf components. We are currently using the WorkBench to construct integrated environments for Haskell program development and for specification and proof of Z specifications.
Haskell All-In-One
This Haskell utility takes a program implemented in multiple modules and converts it to a single module.

Integrated Development Environments

This IDE supports many languages. For Haskell it currently supports project management, syntax highlighting, building (with GHC) & executing within the IDE.
Haskell support for Eclipse
Eclipse is an open, extensible IDE platform for 'everything and nothing in particular'. It is implemented in Java and runs on several platforms. The Java IDE built on top of it has already become very popular among Java developers. The Haskell tools extend it to support editing (syntax coloring, code assist), compiling, and running Haskell programs from within the IDE. More features like source code navigation, module browsing etc. will be added in the future.
hIDE is a GUI-based Haskell IDE written using gtk+hs. It does not include an editor but instead interfaces with NEdit, vim or GNU emacs.
Through the dark ages many a programmer has longed for the ultimate tool. In response to this most unnerving craving, of which we ourselves have had maybe more than our fair share, the dynamic trio of #Haskellaniacs (dons, dcoutts and Lemmih) hereby announce, to the relief of the community, that a fetus has been conceived: hIDE - the Haskell Integrated Development Environment. So far the unborn integrates source code recognition and a chameleon editor, resenting these in a snappy gtk2 environment. Although no seer has yet predicted the date of birth of our hIDEous creature, we hope that the mere knowledge of its existence will spread peace of mind throughout the community as oil on troubled waters. See also: Screenshots of HIDE and HIDE
JCreator with Haskell support
JCreator is a highly customizable Java IDE for Windows. Features include extensive project support, fully customizable toolbars (including the images of user tools) and menus, increase/decrease indent for a selected block of text (tab/shift+tab respectively). The Haskell support module adds syntax highlighting for haskell files and winhugs, hugs, a static checker (if you double click on the error message, JCreator will jump to the right file and line and highlight it yellow) and the Haskell 98 Report as tools. Platforms: Win95, Win98, WinNT and Win2000 (only Win95 not tested yet). Size: 6MB.
JCreator is a trademark of Xinox Software; Copyright © 2000 Xinox Software
The Haskell support module is made by Rijk-Jan van Haaften.
Visual Haskell
Visual Haskell is a complete development environment for Haskell software, based on Microsoft's Microsoft Visual Studio platform. Visual Haskell integrates with the Visual Studio editor to provide interactive features to aid Haskell development, and it enables the construction of projects consisting of multiple Haskell modules, using the Cabal building/packaging infrastructure.

Editor Modes for syntax highlighting and more

For SubEthaEdit (Mac OS X editor):
Haskell mode.
For KDE's Kate
  • Files by Ralf Hinze.
  • [hs.xml hs.xml] and [lhs.xml lhs.xml] by Brian Huffman.
NEdit syntax highlighting and block comment support.
vim syntax highlighting
  • by Don Stewart: for TeX and cpp style Haskell files.
  • by Ian Lynagh: distinguishes different literal Haskell styles.
  • by John Williams: Both regular Haskell [haskell.vim .hs] and [lhaskell.vim .lhs] files that uncomment lines using '>' are supported.
Syntax highlighting file for textpad
by Jeroen van Wolffelaar and Arjan van IJzerdoorn, which inludes all prelude functions, datatype, constructors, etc, all in seperate groups.
Haskell mode
for jed by Marcin 'Qrczak' Kowalczyk.
Haskell Mode for Emacs
Supports font locking, declaration scanning, documentation of types, indentation and interaction with Hugs.
Alternative Hugs Mode for Emacs by Chris Van Humbeeck
Provides fontification and cooperation with Hugs. Updated for emacs 20.* by Adam P. Jenkins.

Some other, mostly obsolete, modes are available in CVS.

Typesetting Haskell in TeX

A TeX package for typesetting literate scripts in TeX. The output looks much like the code from Chris Okasaki's book "Purely Functional Data Structures", doing syntax highlighting and converting ASCII art such as"->" or "alpha" to proper mathematical symbols. It should work with both LaTeX and plain TeX, and it does its magic without any annotations, directly on the source code (lambdaTeX uses an almost-complete Haskell lexical analyzer written entirely in plain TeX). You only have to add \input lambdaTeX at the top of your source file, and manually typeset your literate comments so they look as good as the source code.
Haskell Style for LaTeX2e
by Manuel Chakravarty provides environments and macros that simplify setting Haskell programs in LaTeX.
A preprocessor for typesetting Haskell programs that combines some of the good features of pphs and smugweb. It generates LaTeX code from literate Haskell sources.
--- another tool helping literate programming in Haskell. It helps to maintain views in a literate programming project. For example, it is among the tools used for developing a compiler in an iterative way with manuals didactically reflecting these evolving series of versions deriving from the literal code (see Essential Haskell Compiler project). Thus, Shuffle gives us the possibility for making didactically the evolution of versions visible in the documentation, when this is needed. More generally, Shuffle gives us tangling and weaving possibilities of literate programming. I think it gives a way to think of literal program development in a more abstract way by supporting the concept of views (maybe a too far analogy: version control management -- e.g. darcs -- helps thinking of program development in a more abstract way, too). Shuffle works well together with lhs2tex.
A Latex style file by Andrew Cooke that makes literal programming in Haskell simple.

Source documentation and browsing

Haddock A Haskell Documentation Tool
A tool for automatically generating documentation from annotated Haskell source code. It is primarily intended for documenting libraries, but it should be useful for any kind of Haskell code. Haddock lets you write documentation annotations next to the definitions of functions and types in the source code, in a syntax that is easy on the eye when writing the source code (no heavyweight mark-up). The documentation generated by Haddock is fully hyperlinked - click on a type name in a type signature to go straight to the definition, and documentation, for that type.
IDoc A No Frills Haskell Interface Documentation System
IDoc extracts interface documentation and declarations from Haskell modules based on standard Haskell layout rules and a small number of clues that the programmer embeds in interface comments. These clues have been designed to be visually non-imposing when displaying the source in a text editor. Interface documentation is rendered in standard markup languages (currently, only HTML is supported). IDoc has been designed to be simple to use and install.
HDoc generates documentation in HTML format for Haskell modules. The generated documents are cross linked and include summaries and detailed descriptions for the documented functions, data types, type classes and instance declarations.
This program generates an HTML document showing the module interfaces of a Haskell project. Convenient links are placed for easy browsing of the different modules of the project, and for quick access to the source code.
The Haskell Module Browser(since 10/06/2003: via Internet Archive)
A browser similar to Smaltalk and Eiffel class browsers.


A unit testing framework for Haskell, similar to JUnit for Java. With HUnit, the programmer can easily create tests, name them, group them into suites, and execute them, with the framework checking the results automatically. Test specification is concise, flexible, and convenient.
A tool for testing Haskell programs automatically. The programmer provides a specification of the program, in the form of properties which functions should satisfy, and QuickCheck then tests that the properties hold in a large number of randomly generated cases. Specifications are expressed in Haskell, using combinators defined in the QuickCheck library. QuickCheck provides combinators to define properties, observe the distribution of test data, and define test data generators.
HTF - The Haskell Test Framework
The HTF lets you write HUnit tests and QuickCheck properties in an easy and convenient way. Additionally, the HTF provides a facility for testing programs by running them and comparing the actual output with the expected output (so called "file-based tests"). The HTF uses Template Haskell to collect all tests and properties, so you do not need to write boilerplate code for that purpose. Preprocessor macros provide you with file name and line number information for tests and properties that failed.

Tracing & debugging

Tracing gives access to otherwise invisible information about a computation. Conventional debuggers allow the user to step through the program computation, stop at given points and examine variable contents. This tracing method is quite unsuitable for Haskell, because its evaluation order is complex, function arguments are usually unwieldy large unevaluated expressions and generally computation details do not match the user's high-level view of functions mapping values to values.

Buddha is a declarative debugger for Haskell 98 programs. It presents the evaluation of a Haskell program as a series of function applications. A typical debugging session involves a series of questions and answers. The questions are posed by the debugger, and the answers are provided by the user. The implementation of Buddha is based on program transformation.
A compiler for a subset of Haskell. Running a compiled program creates an evaluation dependency tree as trace, a structure based on the idea of declarative debugging from the logic programming community. A debugging session consists of the user answering a sequence of yes/no questions.
A Haskell program is first transformed by hat-trans and then compiled with nhc98 or ghc. At runtime the program writes a trace file. There are tools for viewing the trace in various ways: Hat-stack shows a virtual stack of redexes. Hat-observe shows top-level functions in the style of Hood. Hat-trail enables exploring a computation backwards, starting from (part of) a faulty output or an error message. Hat-detect provides algorithmic debugging in the style of Freja. Hat-explore allows free navigation through a computation similar to traditional debuggers and algorithmic debugging and slicing.
A library that permits to observe data structures at given program points. It can basically be used like print statements in imperative languages, but the lazy evaluation order is not affected and functions can be observed as well.
"Graphical Hood" - a Java-based graphical observation event viewer, building on Hood.

Data structures

Chris Okasaki is developing a library of efficient data structures. It provides sequences, finite maps, priority queues, and sets/bags. (overview paper).
Binary/BinArray library
A port of Malcolm Wallace's Binary library for NHC13, offering facilities for heap compression and binary I/O. A related library, BinArray, uses Binary to implement imperative binary arrays.
FGL - A Functional Graph Library
The functional graph library provides a collection of graph operations.
A bundle for generic programming. It provides programming support for generic traversal as useful in the implementation of program transformations.
The Haskell STate Preprocessor
This is a short preprocessor for stateful Haskell programs. It aleviates the pain of performing single array lookup/write/update functions with some syntax to support it. It also supports hash table operations based on the HashTable implementation available from the author. Finally, it supports monadic if and monadic case constructions. It is lightweight in the sense that it performs no syntactic analysis and is essentially a character transformer.
Fast Packed Strings
The FPS library provides mmapped and malloc'd packed strings (byte arrays held by a ForeignPtr), along with a list interface to these strings. It lets you do extremely fast IO in Haskell; in some cases, even faster than typical C implementations, as well as conserving space.

Extended Haskell

The purpose of these systems is to enhance the capabilities of Haskell in some way. These are not targeted at any specific application domains.

The PFP library is a collection of modules for Haskell that facilitates probabilistic functional programming, that is, programming with stochastic values. The probabilistic functional programming approach is based on a data type for representing distributions. A distribution represent the outcome of a probabilistic event as a collection of all possible values, tagged with their likelihood. A nice aspect of this system is that simulations can be specified independently from their method of execution. That is, we can either fully simulate or randomize any simulation without altering the code which defines it.
A Haskell extension that extends the normal pattern matching facility with the power of regular expressions.
Ross Patterson has developed a preprocessor that provides a nice notation for Arrows, a generalization of monads.
Functional Reactive Programming
Functional reactive programming integrates time flow into functional programming. This provides an elegant way to express computation in domains such as interactive animations, robotics, computer vision, user interfaces, and simulation. The Yampa system is an implementation of FRP based on arrows.

Interfacing with other languages and systems

HaXR - the Haskell XML-RPC library
An XML-RPC client and server library. XML-RPC is "remote procedure calling using HTTP as the transport and XML as the encoding. XML-RPC is designed to be as simple as possible, while allowing complex data structures to be transmitted, processed and returned."
HAIFA is an implementation of parts of the web-service architecture in Haskell. Notably it includes an XML serializer, a partial implementation of XML Schema and SOAP/1.1.

Tools for interfacing with other languages

The definition of a basic foreign function interface for Haskell (FFI) is finished. It has been agreed on and implemented by most Haskell implementors. The following tools already produce code for this interface. The Guide to Haskell's Foreign Function Interface provides a comparision of the different tools.

Green Card
Green Card is a foreign function interface preprocessor for Haskell, simplifying the task of interfacing Haskell programs to external libraries (which are normally exposed via C interfaces). Green Card is currently able to generate code compatible with the [../implementations.html#ghc Glasgow Haskell Compiler], [../implementations.html#hugs Hugs] and [../implementations.html#nhc nhc].
HaskellDirect is an Interface Definition Language (IDL) compiler for Haskell, which helps interfacing Haskell code to libraries or components written in other languages (C). An IDL specification specifies the type signatures and types expected by a set of external functions. One important use of this language neutral specification of interfaces is to specify COM (Microsoft's Component Object Model) interfaces, and HaskellDirect offers special support for both using COM objects from Haskell and creating Haskell COM objects. HaskellDirect groks both the OSF DCE dialect of IDL (including the various extensions introduced by the Microsoft IDL compiler) and the OMG IIOP/CORBA dialect.
A lightweight tool for implementing access to C libraries from Haskell.
Haskell FFI Binding Modules Generator (HSFFIG) is a tool that takes a C library include file (.h) and generates Haskell Foreign Functions Interface import declarations for items (functions, structures, etc.) the header defines.
A Java Native Interface for Haskell. Allows Haskell to invoke Java code. Includes a tool to generate Haskell bindings for a Java library. Works for hugs and ghc under both Linux and Windows.
Haskell/Java VM Bridge
A bridge to the Java virtual machine via JNI for Haskell.
HaskellScript is the collective name for all Haskell components, both tools and libararies, that allow interaction with the COM/ActiveX framework.
A tool to simplify the process of interfacing C libraries to Haskell. It is less powerful than HaskellDirect, but easier to use and more portable.

Interfaces to specific systems

A library for compiling and loading plugins into a running Haskell program.
A library for using Haskell for tasks which are usually done by shell scripts, e.g. command line parsing, analysing paths, etc.
CGI Library
CGI programs can receive input from the client's web browser, encoded in a complicated fashion, and can write output in a variety of formats (plain text, HTML, JPEG etc) which the client then sees. The decoding and encoding of the IO is often expressed in PERL or C, and makes CGI applications tedious and awkward to write. Haskell/CGI is a library for writing CGI programs in Haskell 1.3 and above.
CGI Library
An all-in-one-file version of Erik Meijer's CGI library (above) with some bugs fixed, a few extensions and ported to Haskell 98.
daVinci binding
A binding to daVinci, an X-Windows based visualization tool for directed graphs.
hMPI is an acronym for HaskellMPI. It is a Haskell binding conforming to MPI (Message Passing Interface) standard 1.1/1.2. The programmer is in full control over the communication between the nodes of a cluster.
Smarty(since 10/06/2003: via Internet Archive)
The world's smartest i/o device for Haskell. An interface between Haskell and Squeak, a freely available Smalltalk language and environment.
A small library, based on runProcess in the standardised posix library. It provides lazy output from subprocesses.
This package allows Haskell programmers to write CORBA clients and servers using the MICO open-source CORBA implementation. It defines a Haskell language mapping for CORBA, and includes an IDL compiler which generates Haskell stub and skeleton modules from IDL files.

Interfacing with databases

HSQL is a simple library which provides an interface to multiple databases. MySQL, PostgreSQL, ODBC, SQLite and Oracle are currently supported. It is part of HToolkit.
A library to interface to the Oracle DBMS. Part of the Haskell-Libs project.
An updated version of Daan Leijen's HaskellDB that works with current Haskell implementations and is relatively platform-independent.
HaskellDB is a combinator library for expressing queries and other operations on relational databases in a type safe and declarative way. All the queries and operations are completely expressed within Haskell, no embedded (SQL) commands are needed. This close integration makes it possible to do arbitrary computations on the database (like computing the transitive closure).
HaSQL is a Haskell to ODBC interface. HaSQL allows Haskell program to run SQL queries against an ODBC compliant database. Queries with parameters are supported. Data is retrieved from the database as a lazy list.
libpq binding
A Haskell binding to libpq, a client-side PostgreSQL programming library, together with a simple DBI for Haskell. It enables the programmer to write database-independent code.

Graphical User Interface and graphics libraries

There exists a large number of gui and graphics libraries for Haskell. Unfortunately there is no standard one and all are more or less incomplete. The following list gives an overview. In general, low-level veneers are going well, but they are low level. High-level abstractions are pretty experimental. There is a need for a supported medium-level GUI library.

High-level: FranTk Fudgets Fruit and wxFruit (Haggis)
Medium-level: wxHaskell Gtk2HS HGL (graphics only) Object I/O
Low-level veneers: HOpenGL (graphics only) TclHaskell Win32 X11

Graphical User Interface Libraries

wxHaskell is a portable and native GUI library built on top of wxWindows - a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. wxWindows is a mature library (in development since 1992) that supports a wide range of widgets with the native look-and-feel, and it has a very active community.
Gtk2Hs is a GUI library for Haskell based on Gtk+. Gtk+ is an extensive and mature multi-platform toolkit for creating graphical user interfaces. Gtk2Hs is actively developed, supporting the latest version of the Gtk+ 2.x series. It provides automatic memory management, Unicode support and also bindings for various Gnome modules. It runs on Windows, Linux, MacOS X, FreeBSD and Solaris.
HToolkit is a portable Haskell library for writing graphical user interfaces (GUI's). The library is built upon a low-level interface that will be implemented for each different target platform. The low-level library is called Port and is currently implemented for GTK and Windows. The middle-level library is named GIO (the Graphical IO library) and is built upon the low-level Port library.
Htk is a typed, portable encapsulation of Tcl/Tk into Haskell. Its distinctive features are the use of Haskell types and type classes for structuring the interface, an abstract notion of event for describing user interaction, and portability across Windows, Unix and Linux.
TclHaskell is a library of functions for writing platform independent, graphical user interfaces in Haskell. The library provides a convenient, abstract and high-level way to write window-oriented applications. It also provides a more low level interface to write primitive Tcl code where helpful.
For Unix and Windows (and Macintosh?).
Fudgets is primarily a Graphical User Interface Toolkit for the functional programming language Haskell and the X Windows system. Fudgets also makes it easy to create client/server applications that communicate via the Internet. For Unix, not Windows.
Another high-level approach to GUI's in Haskell. It is based on the concepts of Functional Reactive Programming and arrows. There is also another implementation of this approach, called wxFruit. It is implemented on top of wxHaskell.
is a library for building GUIs in Haskell. FranTk uses behaviours and events, concepts from Conal Elliot's Functional Reactive Animation. FranTk provides good support for developing complex dynamic systems, and is built on top of Tcl-Tk. This makes it platform independent. FranTk was developed by Meurig Sage.
For Unix and Windows.
Object I/O for Haskell
A port of Clean Object I/O library for Haskell
A Haskell binding to the NCurses library, a library of functions that manage an application's display on character-cell terminals. hscurses also provides some basic widgets implemented on top of the ncurses binding, such as a text input widget and a table widget.
A minimal binding to curses (as well as ncurses). Smaller and less featured than hscurses, it also provides fast packed string support.

Unsupported GUI-libraries

The following libraries seem to be no longer maintained. However, someone might pick up one of them or at least profit from some design ideas.

Gtk+HS a Haskell binding for GTK+
This library provides a transcription of the original GTK+ API into Haskell. GTK+ is a modern, portable GUI library and forms the basis of the Gnome desktop project. The binding, while not complete, covers most of GTK+'s core functionality and is ready for use in applications that require a GUI of medium complexity.
Developed under Unix, but should also be usable with the Windows port of GTK+.
A functional wrapper on top of GTK+HS that provides convenience functions for frequently used programming patterns and eliminates the need for explicit mutable variables.
Haggis is a graphical user interface framework for the functional language Haskell, running under the X Window system. It is being developed using the Glasgow Haskell Compiler with its concurrent extensions to achieve more comfortable interaction with the outside world.
is a concurrent, strongly typed and higher order encapsulation of Tk that supports the definition of user dialogues. Einar Karlsson developed it for his UniForm WorkBench.
developed by Enno Scholz unifies pictures and widgets in a constraint-based framework for concurrent functional GUI programming.
A library of Fudget-like combinators based on the Openlook widget library was developed by Alastair Reid and Satnam Singh. The code has suffered tremendous bit-rot (does anyone have a copy of ghc-0.16?) but all the reusable ideas are described in the paper.
Embracing Windows
is a framework for developing graphical user interfaces. It runs under Windows 95 using a modified version of Hugs 1.3.
Lazy functional components for graphical user interfaces, developed by Rob Noble under the supervision of Colin Runciman (LNCS 982, pages 321-340).


The Hugs Graphics Library
The Hugs Graphics Library supports 2-dimensional graphics operations, timers, mouse and keyboard actions and multiple windows. It runs on Hugs under both Win32 and X11. An earlier version was used for early prototypes of Fran.
Scalable Vector Graphics for Haskell. Portable, device-independent, resolution-independent library, including support for affine transformations, Bezier curves, fine-grained control of pen attributes, bounds and intersection tests, constructive area geometry, anti-aliased rendering, outline fonts, etc.
Functional Metapost
Functional Metapost is a Haskell binding for MetaPost, the powerful but cumbersome graphics language.
Functional Reactive Animation
FRAN is a Haskell library (or "embedded language") for interactive animations with 2D and 3D graphics and sound. It runs on Hugs under Windows 95 and Windows NT, using Win32 graphics (GDI).
An embedded language and highly optimizing compiler for image synthesis and transformation, based on the simple idea of images as functions over infinite, continuous 2D space. The resulting binaries can be used as PhotoShop plugins, embedded in web pages or PowerPoint, or used in an interactive standalone viewer. The compiler contains no domain-specific knowledge, so it's very extensible. See the gallery for visual examples. Currently Windows-only, but ports are encouraged.
Pan# is a slightly re-engineered version of Pan. It uses the same compiler but used the Microsoft .NET framework instead of visual studio, making it easier to install and use. It also has a number of new features added. While Pan is embedded in Haskell, Pan# has its own Haskell-like language built in so there is no need to use other Haskell compilers. Currently Windows-only.
Pancito is a Haskell module for manipulating functional images and then saving them to disk. It was inspired by Pan.
HOpenGL is a Haskell binding for the OpenGL graphics API (GL 1.2.1 / GLU 1.3) and the portable OpenGL utility toolkit GLUT.

Graphics File Formats

Gif Writer(since 10/06/2003: via Internet Archive; this library is no longer available!)
A simple tool - capable of producing GIF based plots from within Haskell programs. Such plots can be then incorporated into HTML reports, to literate Haskell programs, or to combination of both.
Functional Specification of the JPEG algorithm, and an Implementation for Free
JPEG encoding Written in Gofer.


HTTP and Browser Modules
A significantly RFC compliant HTTP/1.1 implementation. This is an updated version of Warrick Gray's original version.
A family of combinator libraries for programming Web applications. WASH/HTML is for generating dynamic HTML documents, combining flexibility and safety. WASH/CGI is for server-side Web scripting with sessions, compositional forms, and graphics.
HaXml: utilities for using XML with Haskell
Includes an XML parser, an HTML parser, a pretty-printer, a combinator library for generic XML transformations, and two Haskell>-<XML converters using type-based translation.
The Haskell Html Library by Andy Gill
This library is a collection of combinators, allowing your Haskell programs to generate HTML.
Haskell XML Toolbox
The Haskell XML Toolbox bases on the ideas of HaXml and HXML, but introduces a more general approach for processing XML with Haskell. The Haskell XML Toolbox uses a generic data model for representing XML documents, including the DTD subset and the document subset, in Haskell.
CGI Library
CGI programs can receive input from the client's web browser, encoded in a complicated fashion, and can write output in a variety of formats (plain text, HTML, JPEG etc) which the client then sees. The decoding and encoding of the IO is often expressed in PERL or C, and makes CGI applications tedious and awkward to write. Haskell/CGI is a library for writing CGI programs in Haskell 1.3 and above.
CGI Library
An all-in-one-file version of Erik Meijer's CGI library (above) with some bugs fixed, a few extensions and ported to Haskell 98.
Generative Implementation Strategies for Data-Centric Web Applications
Generic presentation layer abstractions of administrative web applications are the central theme of this thesis. The domain-engineering approach results in a framework to support user interfaces generated from high-level descriptions. A domain-specific language describes user interfaces. The [ Haskell-based generator] transforms these descriptions to user interfaces implemented with JavaScript and XHTML.
Haskell Server Pages
Using Haskell as a server-side scripting language, extended to allow embedded XML/XHTML fragments in Haskell code.

Pretty-printer libraries

Pretty printer library
Simon Peyton Jones made an "industrial strength" pretty printing library in Haskell, based on John Hughes's paper "The Design of a Pretty-printing Library" (in Advanced Functional Programming, Johan Jeuring and Erik Meijer (eds), LNCS 925). <a href="">Original version by John Hughes</a>.
Pretty-printing combinators
The combinators in the library are optimal in the sense that they produce the layout with the smallest height possible. They also allow the programmer to specify several different layouts.
PPrint is an implementation of the pretty printing combinators described by Philip Wadler. The PPrint library adds new primitives to describe commonly occuring layouts and works well in practice.

Compiler and compilation tools

Manuel Chakravarty's Compiler Toolkit
There is a significant set of functionality that is required in each compiler like symbol table management, input-output operations, error management, and so on, which are good candidates for code reuse. The Compiler Toolkit is an attempt to provide an open collection of modules for these recurring tasks in Haskell.
The Zephyr Abstract Syntax Description Lanuguage (ASDL)
ASDL is a language designed to describe the tree-like data structures in compilers. Its main goal is to provide a method for compiler components written in different languages to interoperate. ASDL makes it easier for applications written in a variety of programming languages to communicate complex recursive data structures. asdlGen is a tool that takes ASDL descriptions and produces implementations of those descriptions in C, C++, Java, Standard ML, and Haskell.
Typing Haskell in Haskell
A Haskell program that implements a Haskell typechecker, thus providing a mathematically rigorous specification in a notation that is familiar to Haskell users.
Hatchet is a type checking and inference tool for Haskell 98, written in (almost) Haskell 98.
The BNF Converter
A High-Level Tool for Implementing Well-Behaved Programming Languages.
ATerm Library
ATerms provide a generic format for representation and exchange of (annotated) terms. ATerms were developed in the context of the ASF+SDF Meta-Environment. They are also used by the rewriting language Stratego, by the transformation tool bundle XT, by the visitor generator JJForester, and by numerous other tools developed at CWI, Universiteit Utrecht, and elsewhere.
Attribute Grammar
How can attribute grammars help at the separation of concerns, at things related to the goals of aspect oriented programming? How do they relate to other concepts like monads and arrows? Why are they important for the functional programmer? See Wouter Swierstra's WhyAttributeGrammarsMatter. Utrecht University's Attribute Grammar System tools include also an attribute grammar compiler, UUAGC. The concept of attribute grammar was used in their Essential Haskell Compiler project, which gives us not only a working programming language, but also a good didactical material about using attribute grammars, e.g. in writing compilers.

Scanner and parser generators

Happy is a parser generator system for Haskell, similar to the tool `yacc' for C. Like `yacc', it takes a file containing an annotated BNF specification of a grammar and produces a Haskell module containing a parser for the grammar.
Frown is an LALR(k) parser generator for Haskell 98 written in Haskell 98.
A parser generator for Haskell using monadic parser combinators. It was developed to be compatible with Happy.
Utrecht Parser Combinator Library
The combinators in this library analyse the grammar on the fly and build parsers that are quite efficient. An interesting aspect is that parsing results become available on the fly without hanging on to the input. The parsers will give extensive error reports of erroneous situations, and wil proceed with parsing.
A simple, well documented monadic parser combinator library for fast parsers with good error messages.
A parser for Haskell written purely in Haskell (using the Happy parser generator).
Standalone distribution of the self-optimising lexer (i.e. regex) and parser combinators of the Compiler Toolkit (CTK).
Alex: A Lexical Analyser Generator
Alex 2.0 is a Lex-like package for generating Haskell scanners.
The Haskell Dynamic Lexer Engine
This system is completely dynamic: the lexer may be modified at runtime, and string buffers may be lexed by different lexers at different times.


The Haskore Computer Music System
Haskore is a collection of Haskell modules designed for expressing musical structures in the high-level, declarative style of functional programming. Haskore is a means for describing music - in particular Western Music - rather than sound. It is not a vehicle for synthesizing sound produced by musical instruments, for example, although it does capture the way certain (real or imagined) instruments permit control of dynamics and articulation. Haskore compositions can be translated into various executable formats like MIDI and printed in traditional notation.
A set of Haskell modules written on top of Haskore to make it easier to sequence simple, repetitive music.

Numerical algorithms and mathematics

The Library for Geometric Algorithms
is a small Haskell library, that contains algorithms for two-dimensional convex hulls, triangulations of polygons, Voronoi-diagrams and Delaunay-triangulations, the QEDS data structure, kd-trees and range-trees.
Libraries for digital signal processing
Modules for matrix manpulation, digital signal processing, spectral stimation, and frequency estimation.
Papers by Jerzy Karczmarczuk
Some interesting uses of Haskell in mathematics, including functional differentiation.
Algebraic Domain Constructor
The HaskellMath library is a sandbox for me to experiment with mathematics algorithms. So far I've implemented a few quantitative finance models (Black Scholes and Binomial Trees) and basic linear algebra functions. Next I'll probably work on linear programming (simplex and interior point methods), and then I may return to more quantitative finance. All comments welcome!
Wrapper to CLAPACK
Wrapper to GSL matrix routines
Numeric Prelude
Experimental revised framework for numeric type classes.
mirror of the following numeric modules of Jan Skibinski
Numerics with fractions(since 10/06/2003: via Internet Archive)
Roots of polynomials(since 10/06/2003: via Internet Archive)
It implements the well known Laguerre's method for finding complex roots of polynomials.
Indexless linear algebra algorithms(since 10/06/2003: via Internet Archive)
Orthogonalization, solution of linear equations, eigenvalues and eigenvectors.
State vector evolution(since 10/06/2003: via Internet Archive)
Short study of fuzzy oscillator(since 10/06/2003: via Internet Archive)
N-dimensional tensors(since 10/06/2003: via Internet Archive)

Hardware verification

Hawk, Specifying and Prototyping Microprocessors
The goal of the Hawk project is to develop a language for expressing highly abstracted specifications of modern microprocessor designs, to provide design teams with the ability to dynamically explore a wide range of design choices. The Hawk language is Haskell plus the Hawk library.
Lava is a hardware description language based upon Haskell.


Haskell for Vision and Robotics
Frob is an Embedded Domain Specific Language for controlling robots. It is built using the principals of Functional Reactive Programming, as developed by Conal Elliott for the Fran animation system. The current incarnation of Frob is part of the Yampa FRP system.

Cognitive Science

(Tools, algorithms, frameworks, paradigms concerning Genetic Programming, Artificial Intelligence, Neural Networks, Fuzzy Logic, Natural Language Processing etc.)
Genetic programming
Dr. Tina Yu's publications, many of them on fruitful applications of Functional Programming in Genetic Programming. Deryck F. Brown, A. Beatriz Garmendia-Doval and John A. W. McCall, A Genetic Algorithm Framework Using Haskell
Natural language processing
Articles and/or projects on linguistic theories concerning Haskell, combinatory logic, e.g.


Editor combinators allow to assemble structure editors compositionally instead of generating them from descriptions, just as parsing combinators allow to assemble parsers compositionally instead of employing parser generators to generate parsers from grammar descriptions.
Expander2 is a flexible multi-purpose workbench for rewriting, verification, constraint solving, flow graph analysis and related procedures that build up proofs or computation sequences. Moreover, tailor-made interpreters display terms as 2D structures ranging from trees and rooted graphs to tables, fractals and other turtle-system-generated pictures.
Strafunski is a Haskell bundle that provides support for generic programming in Haskell, based on the concept of a functional strategy. It consists of a combinator library (StrategyLib) and a precompiler (DrIFT-Strafunski).
FunGEn - a game engine for Haskell
FunGEn (Functional Game Engine) is a 2D platform-independent game engine implemented in and for Haskell, using HOpenGL. It is intended to help game programmers in the game development process, in a faster and automated way.
The Haskell Cryptographic Library
A library of cryptographic functions collected together in one package.
A number theory library, RSA library, and RSA programs.
Implementations of MD5, SHA1 and DES
Regular expression library
Inspired by the Perl regular expression library, written purely in Haskell. Also part of the GHC distribution.
Partial v0.1
The Partial library provides a partial order class. It also provides routines for generating a Hasse diagram from a set and a partial order. Renderers are provided for the abstract Hasse diagram representation into LaTeX (via Xy-pic) and into dot, the format for AT&T's Graphviz tools. Since no horizontal sorting is done, the Xy-pic output is rather poor at present; dot does a much better job with its layout optimisation algorithm.
fun->pdf(since 10/06/2003: via Internet Archive)
An implementation of a PDF dynamic writer in Haskell.
A module for GNU-/POSIX-like option handling of commandline arguments

Collections of libraries

Libraries for other languages

If you are thinking about designing a new library for Haskell, you ought to look what has been done in other languages. Here are standard library definitions for