Haskell () is a
general-purpose,
statically typed
In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a ''type'' (for example, integer, floating point, string) to every '' term'' (a word, phrase, or other set of symbols). Usu ...
,
purely functional programming language
A programming language is a system of notation for writing computer programs.
Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
with
type inference
Type inference, sometimes called type reconstruction, refers to the automatic detection of the type of an expression in a formal language. These include programming languages and mathematical type systems, but also natural languages in some bran ...
and
lazy evaluation
In programming language theory, lazy evaluation, or call-by-need, is an evaluation strategy which delays the evaluation of an Expression (computer science), expression until its value is needed (non-strict evaluation) and which avoids repeated eva ...
. Designed for teaching, research, and industrial applications, Haskell pioneered several programming language
features such as
type class
In computer science, a type class is a type system construct that supports ad hoc polymorphism. This is achieved by adding constraints to type variables in parametrically polymorphic types. Such a constraint typically involves a type class T a ...
es, which enable
type-safe operator overloading, and
monadic input/output
In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...
(IO). It is named after
logic
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure o ...
ian
Haskell Curry. Haskell's main implementation is the
Glasgow Haskell Compiler (GHC).
Haskell's
semantics
Semantics is the study of linguistic Meaning (philosophy), meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction betwee ...
are historically based on those of the
Miranda programming language, which served to focus the efforts of the initial Haskell working group. The last formal specification of the language was made in July 2010, while the development of GHC continues to expand Haskell via language extensions.
Haskell is used in academia and industry. , Haskell was the 28th most popular programming language by
Google search
Google Search (also known simply as Google or Google.com) is a search engine operated by Google. It allows users to search for information on the World Wide Web, Web by entering keywords or phrases. Google Search uses algorithms to analyze an ...
es for tutorials, and made up less than 1% of active users on the
GitHub
GitHub () is a Proprietary software, proprietary developer platform that allows developers to create, store, manage, and share their code. It uses Git to provide distributed version control and GitHub itself provides access control, bug trackin ...
source code repository.
History
After the release of
Miranda by Research Software Ltd. in 1985, interest in lazy functional languages grew. By 1987, more than a dozen non-
strict, purely functional programming languages existed. Miranda was the most widely used, but it was
proprietary software
Proprietary software is computer software, software that grants its creator, publisher, or other rightsholder or rightsholder partner a legal monopoly by modern copyright and intellectual property law to exclude the recipient from freely sharing t ...
. At the conference on
Functional Programming Languages and Computer Architecture (FPCA '87) in
Portland, Oregon
Portland ( ) is the List of cities in Oregon, most populous city in the U.S. state of Oregon, located in the Pacific Northwest region. Situated close to northwest Oregon at the confluence of the Willamette River, Willamette and Columbia River, ...
, there was a strong consensus that a committee be formed to define an
open standard
An open standard is a standard that is openly accessible and usable by anyone. It is also a common prerequisite that open standards use an open license that provides for extensibility. Typically, anybody can participate in their development due to ...
for such languages. The committee's purpose was to consolidate existing
functional languages into a common one to serve as a basis for future research in functional-language design.
Haskell 1.0 to 1.4
Haskell was developed by a committee, attempting to bring together off the shelf solutions where possible.
Type classes, which enable
type-safe operator overloading, were first proposed by
Philip Wadler and Stephen Blott to address the ad-hoc handling of equality types and arithmetic overloading in languages at the time.
In early versions of Haskell up until and including version 1.2, user interaction and
input/output
In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...
(IO) were handled by both streams based and continuation based mechanisms which were widely considered unsatisfactory. In version 1.3,
monadic IO was introduced, along with the generalisation of type classes to higher kinds (type constructors). Along with "do notation", which provides syntactic sugar for the Monad type class, this gave Haskell an effect system that maintained referential transparency and was convenient.
Other notable changes in early versions were the approach to the 'seq' function, which creates a data dependency between values, and is used in lazy languages to avoid excessive memory consumption; with it moving from a type class to a standard function to make refactoring more practical.
The first version of Haskell ("Haskell 1.0") was defined in 1990. The committee's efforts resulted in a series of language definitions (1.0, 1.1, 1.2, 1.3, 1.4).
Haskell 98
In late 1997, the series culminated in ''Haskell 98'', intended to specify a stable, minimal, portable version of the language and an accompanying standard
library
A library is a collection of Book, books, and possibly other Document, materials and Media (communication), media, that is accessible for use by its members and members of allied institutions. Libraries provide physical (hard copies) or electron ...
for teaching, and as a base for future extensions. The committee expressly welcomed creating extensions and variants of Haskell 98 via adding and incorporating experimental features.
In February 1999, the Haskell 98 language standard was originally published as ''The Haskell 98 Report''. In January 2003, a revised version was published as ''Haskell 98 Language and Libraries: The Revised Report''. The language continues to evolve rapidly, with the
Glasgow Haskell Compiler (GHC) implementation representing the current ''de facto'' standard.
Haskell 2010
In early 2006, the process of defining a successor to the Haskell 98 standard, informally named ''Haskell Prime'', began. This was intended to be an ongoing incremental process to revise the language definition, producing a new revision up to once per year. The first revision, named ''Haskell 2010'', was announced in November 2009
[ and published in July 2010.
Haskell 2010 is an incremental update to the language, mostly incorporating several well-used and uncontroversial features previously enabled via compiler-specific flags.
* Hierarchical module names. Module names are allowed to consist of dot-separated sequences of capitalized identifiers, rather than only one such identifier. This lets modules be named in a hierarchical manner (e.g., ]Data.List
instead of List
), although technically modules are still in a single monolithic namespace. This extension was specified in an addendum to Haskell 98 and was in practice universally used.
* The foreign function interface (FFI) allows bindings to other programming languages. Only bindings to C are specified in the Report, but the design allows for other language bindings. To support this, data type declarations were permitted to contain no constructors, enabling robust nonce types for foreign data that could not be constructed in Haskell. This extension was also previously specified in an Addendum to the Haskell 98 Report and widely used.
* So-called ''n''+''k'' patterns (definitions of the form fact (n+1) = (n+1) * fact n
) were no longer allowed. This syntactic sugar
In computer science, syntactic sugar is syntax within a programming language that is designed to make things easier to read or to express. It makes the language "sweeter" for human use: things can be expressed more clearly, more concisely, or in an ...
had misleading semantics, in which the code looked like it used the (+)
operator, but in fact desugared to code using (-)
and (>=)
.
* The rules of type inference
Type inference, sometimes called type reconstruction, refers to the automatic detection of the type of an expression in a formal language. These include programming languages and mathematical type systems, but also natural languages in some bran ...
were relaxed to allow more programs to type check.
* Some syntax
In linguistics, syntax ( ) is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure (constituenc ...
issues (changes in the formal grammar) were fixed: pattern guards were added, allowing pattern matching within guards; resolution of operator fixity was specified in a simpler way that reflected actual practice; an edge case in the interaction of the language's lexical syntax of operators and comments was addressed, and the interaction of do-notation and if-then-else was tweaked to eliminate unexpected syntax errors.
* The LANGUAGE
pragma was specified. By 2010, dozens of extensions to the language were in wide use, and GHC (among other compilers) provided the LANGUAGE
pragma to specify individual extensions with a list of identifiers. Haskell 2010 compilers are required to support the Haskell2010
extension and are encouraged to support several others, which correspond to extensions added in Haskell 2010.
Future standards
The next formal specification had been planned for 2020.[ On 29 October 2021, with GHC version 9.2.1, the GHC2021 extension was released. While this is not a formal language spec, it combines several stable, widely-used GHC extensions to Haskell 2010.][GHC 2020 Team (29 October 2021]
GHC 9.2.1
released
Features
Haskell features lazy evaluation
In programming language theory, lazy evaluation, or call-by-need, is an evaluation strategy which delays the evaluation of an Expression (computer science), expression until its value is needed (non-strict evaluation) and which avoids repeated eva ...
, lambda expressions, pattern matching
In computer science, pattern matching is the act of checking a given sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually must be exact: "either it will or will not be a ...
, list comprehension, type class
In computer science, a type class is a type system construct that supports ad hoc polymorphism. This is achieved by adding constraints to type variables in parametrically polymorphic types. Such a constraint typically involves a type class T a ...
es and type polymorphism. It is a purely functional programming
In computer science, purely functional programming usually designates a programming paradigm—a style of building the structure and elements of computer programs—that treats all computation as the evaluation of function (mathematics), mathematic ...
language, which means that functions generally have no side effects
In medicine, a side effect is an effect of the use of a medicinal drug or other treatment, usually adverse but sometimes beneficial, that is unintended. Herbal and traditional medicines also have side effects.
A drug or procedure usually used ...
. A distinct construct exists to represent side effects, orthogonal
In mathematics, orthogonality (mathematics), orthogonality is the generalization of the geometric notion of ''perpendicularity''. Although many authors use the two terms ''perpendicular'' and ''orthogonal'' interchangeably, the term ''perpendic ...
to the type of functions. A pure function can return a side effect that is subsequently executed, modeling the impure functions of other languages.
Haskell has a strong, static type system based on Hindley–Milner type inference. Its principal innovation in this area is type classes, originally conceived as a principled way to add overloading to the language, but since finding many more uses.
The construct that represents side effects is an example of a monad: a general framework which can model various computations such as error handling, nondeterminism, parsing
Parsing, syntax analysis, or syntactic analysis is a process of analyzing a String (computer science), string of Symbol (formal), symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal gramm ...
and software transactional memory. They are defined as ordinary datatypes, but Haskell provides some syntactic sugar
In computer science, syntactic sugar is syntax within a programming language that is designed to make things easier to read or to express. It makes the language "sweeter" for human use: things can be expressed more clearly, more concisely, or in an ...
for their use.
Haskell has an open, published specification, and multiple implementations exist. Its main implementation, the Glasgow Haskell Compiler (GHC), is both an interpreter and native-code compiler
In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primaril ...
that runs on most platforms. GHC is noted for its rich type system incorporating recent innovations such as generalized algebraic data type
In functional programming, a generalized algebraic data type (GADT, also first-class phantom type, guarded recursive datatype, or equality-qualified type) is a generalization of a Parametric polymorphism, parametric algebraic data type (ADT).
Ove ...
s and type families. The Computer Language Benchmarks Game also highlights its high-performance implementation of concurrency and parallelism.[Computer Language Benchmarks Game](_blank)
/ref>
An active, growing community exists around the language, and more than 5,400 third-party open-source libraries and tools are available in the online package repository ''Hackage''.
Code examples
A "Hello, World!" program
A "Hello, World!" program is usually a simple computer program that emits (or displays) to the screen (often the Console application, console) a message similar to "Hello, World!". A small piece of code in most general-purpose programming languag ...
in Haskell (only the last line is strictly necessary):
module Main (main) where -- not needed in interpreter, is the default in a module file
main :: IO () -- the compiler can infer this type definition
main = putStrLn "Hello, World!"
The factorial
In mathematics, the factorial of a non-negative denoted is the Product (mathematics), product of all positive integers less than or equal The factorial also equals the product of n with the next smaller factorial:
\begin
n! &= n \times ...
function in Haskell, defined in a few different ways (the first line is the type annotation, which is optional and is the same for each implementation):
factorial :: (Integral a) => a -> a
-- Using recursion (with the "ifthenelse" expression)
factorial n = if n < 2
then 1
else n * factorial (n - 1)
-- Using recursion (with pattern matching)
factorial 0 = 1
factorial n = n * factorial (n - 1)
-- Using recursion (with guards)
factorial n
, n < 2 = 1
, otherwise = n * factorial (n - 1)
-- Using a list and the "product" function
factorial n = product ..n
-- Using fold (implements "product")
factorial n = foldl (*) 1 ..n
-- Point-free style
factorial = foldr (*) 1 . enumFromTo 1
Using Haskell's Fixed-point combinator allows this function to be written without any explicit recursion.
import Data.Function (fix)
factorial = fix fac
where fac f x
, x < 2 = 1
, otherwise = x * f (x - 1)
As the ''Integer'' type has arbitrary-precision, this code will compute values such as factorial 100000
(a 456,574-digit number), with no loss of precision.
An implementation of an algorithm similar to quick sort
Quicksort is an efficient, general-purpose sorting algorithm. Quicksort was developed by British computer scientist Tony Hoare in 1959 and published in 1961. It is still a commonly used algorithm for sorting. Overall, it is slightly faster than ...
over lists, where the first element is taken as the pivot:
-- Type annotation (optional, same for each implementation)
quickSort :: Ord a => ->
-- Using list comprehensions
quickSort [] = [] -- The empty list is already sorted
quickSort (x:xs) = quickSort [a , a <- xs, a < x] -- Sort the left part of the list
++ [x] ++ -- Insert pivot between two sorted parts
quickSort a <- xs, a >= x -- Sort the right part of the list
-- Using filter
quickSort [] = []
quickSort (x:xs) = quickSort (filter (=x) xs)
Implementations
All listed implementations are distributed under open source licenses.["Implementations"](_blank)
at the Haskell Wiki
Implementations that fully or nearly comply with the Haskell 98 standard include:
* The Glasgow Haskell Compiler (GHC) compiles to native code on many different processor architectures, and to ANSI C, via one of two intermediate languages: C--, or in more recent versions, LLVM
LLVM, also called LLVM Core, is a target-independent optimizer and code generator. It can be used to develop a Compiler#Front end, frontend for any programming language and a Compiler#Back end, backend for any instruction set architecture. LLVM i ...
(formerly Low Level Virtual Machine) bitcode. GHC has become the ''de facto'' standard Haskell dialect. There are libraries (e.g., bindings to OpenGL
OpenGL (Open Graphics Library) is a Language-independent specification, cross-language, cross-platform application programming interface (API) for rendering 2D computer graphics, 2D and 3D computer graphics, 3D vector graphics. The API is typic ...
) that work only with GHC. GHC was also distributed with the Haskell platform. GHC features an asynchronous runtime that also schedules threads across multiple CPU cores similar to the Go runtime.
* Jhc, a Haskell compiler written by John Meacham, emphasizes speed and efficiency of generated programs and exploring new program transformations.
** Ajhc is a fork of Jhc.
* The Utrecht Haskell Compiler (UHC) is a Haskell implementation from Utrecht University
Utrecht University (UU; , formerly ''Rijksuniversiteit Utrecht'') is a public university, public research university in Utrecht, Netherlands. Established , it is one of the oldest universities in the Netherlands. In 2023, it had an enrollment of ...
. It supports almost all Haskell 98 features plus many experimental extensions. It is implemented using attribute grammars and is primarily used for research on generated type systems and language extensions.
Implementations no longer actively maintained include:
* The Haskell User's Gofer System ( Hugs) is a bytecode
Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (normal ...
interpreter. It was once one of the implementations used most widely, alongside the GHC compiler, but has now been mostly replaced by GHCi. It also comes with a graphics library.
* HBC is an early implementation supporting Haskell 1.4. It was implemented by Lennart Augustsson in, and based on, Lazy ML
Lennart Augustsson is a Sweden, Swedish computer scientist. He was formerly a lecturer at the computer science, Computing Science Department at Chalmers University of Technology. His research field is functional programming and implementations of ...
. It has not been actively developed for some time.
* nhc98 is a bytecode compiler focusing on minimizing memory use.
** The York Haskell Compiler ( Yhc) was a fork of nhc98, with the goals of being simpler, more portable and efficient, and integrating support for Hat, the Haskell tracer. It also had a JavaScript
JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior.
Web browsers have ...
backend, allowing users to run Haskell programs in web browser
A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...
s.
Implementations not fully Haskell 98 compliant, and using a variant Haskell language, include:
* Eta and Frege are dialects of Haskell targeting the Java virtual machine
A Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode. The JVM is detailed by a specification that formally descr ...
.
* Gofer is an educational dialect of Haskell, with a feature called ''constructor classes'', developed by Mark Jones. It is supplanted by Haskell User's Gofer System (Hugs).
* Helium, a newer dialect of Haskell. The focus is on making learning easier via clearer error messages by disabling type classes as a default.
Notable applications
* Agda is a proof assistant written in Haskell.
*Cabal
A cabal is a group of people who are united in some close design, usually to promote their private views or interests in an ideology, a state (polity), state, or another community, often by Wiktionary:intrigue, intrigue and usually without the kn ...
is a tool for building
A building or edifice is an enclosed Structure#Load-bearing, structure with a roof, walls and window, windows, usually standing permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, a ...
and packaging Haskell libraries and programs.
* Darcs is a revision control system written in Haskell, with several innovative features, such as more precise control of patches to apply.
* Glasgow Haskell Compiler (GHC) is also often a testbed for advanced functional programming features and optimizations in other programming languages.
* Git-annex is a tool to manage (big) data files under Git version control. It also provides a distributed file synchronization system (git-annex assistant).
* Linspire Linux chose Haskell for system tools development.
* Pandoc is a tool to convert one markup format into another.
* Pugs is a compiler
In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primaril ...
and interpreter for the programming language
A programming language is a system of notation for writing computer programs.
Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
then named Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language".
Perl was developed ...
6, but since renamed Raku.
*TidalCycles
TidalCycles (also known as Tidal) is a live coding environment which is designed for improvising and composing music. Technically, it is a domain-specific language embedded in the functional programming language Haskell, and is focused on the g ...
is a domain special language for live coding musical patterns, embedded in Haskell.
* Xmonad is a window manager
A window manager is system software that controls the placement and appearance of window (computing), windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment. They ...
for the X Window System
The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems.
X originated as part of Project Athena at Massachusetts Institute of Technology (MIT) in 1984. The X protocol has been at ...
, written fully in Haskell.
*GarganText is a collaborative tool to map through semantic analysis texts on any web browser
A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...
, written fully in Haskell and PureScript, which is used for instance in the research community to draw up state-of-the-art reports and roadmaps.
Industry
* Bluespec SystemVerilog (BSV) is a language extension of Haskell, for designing electronics
Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...
. It is an example of a domain-specific language embedded into Haskell. Further, Bluespec, Inc.'s tools are implemented in Haskell.
* Cryptol, a language and toolchain for developing and verifying cryptography
Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...
algorithms, is implemented in Haskell.
* Facebook
Facebook is a social media and social networking service owned by the American technology conglomerate Meta Platforms, Meta. Created in 2004 by Mark Zuckerberg with four other Harvard College students and roommates, Eduardo Saverin, Andre ...
implements its anti-spam programs in Haskell, maintaining the underlying data access library as open-source software
Open-source software (OSS) is Software, computer software that is released under a Open-source license, license in which the copyright holder grants users the rights to use, study, change, and Software distribution, distribute the software an ...
.
*The Cardano blockchain platform is implemented in Haskell.
*GitHub
GitHub () is a Proprietary software, proprietary developer platform that allows developers to create, store, manage, and share their code. It uses Git to provide distributed version control and GitHub itself provides access control, bug trackin ...
implemented Semantic
Semantics is the study of linguistic Meaning (philosophy), meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction betwee ...
, an open-source library for analysis, diffing, and interpretation of untrusted source code, in Haskell.
* Standard Chartered's financial modelling language Mu is syntactic Haskell running on a strict runtime.
* seL4, the first formally verified microkernel
In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, ...
,[
A formal proof of functional correctness was completed in 2009.
] used Haskell as a prototyping language for the OS developer.[ At the same time, the Haskell code defined an executable specification with which to reason, for automatic translation by the theorem-proving tool.][ The Haskell code thus served as an intermediate prototype before final C refinement.][
* Target stores' supply chain optimization software is written in Haskell.
* Co–Star
* Mercury Technologies' back end is written in Haskell.
]
Web
Notable web framework
A web framework (WF) or web application framework (WAF) is a software framework that is designed to support the development of web applications including web services, web resources, and web APIs. Web frameworks provide a standard way to build a ...
s written for Haskell include:
* IHP
* Servant
A domestic worker is a person who works within a residence and performs a variety of household services for an individual, from providing cleaning and household maintenance, or cooking, laundry and ironing, or care for children and elderly ...
* Snap
* Yesod
Criticism
Jan-Willem Maessen, in 2002, and Simon Peyton Jones, in 2003, discussed problems associated with lazy evaluation while also acknowledging the theoretical motives for it. In addition to purely practical considerations such as improved performance, they note that lazy evaluation makes it more difficult for programmers to reason about the performance of their code (particularly its space use).
Bastiaan Heeren, Daan Leijen, and Arjan van IJzendoorn in 2003 also observed some stumbling blocks for Haskell learners: "The subtle syntax and sophisticated type system of Haskell are a double edged sword—highly appreciated by experienced programmers but also a source of frustration among beginners, since the generality of Haskell often leads to cryptic error messages." To address the error messages researchers from Utrecht University developed an advanced interpreter called Helium
Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
, which improved the user-friendliness of error messages by limiting the generality of some Haskell features. In particular it disables type classes by default.
Ben Lippmeier designed Disciple as a strict-by-default (lazy by explicit annotation) dialect of Haskell with a type-and-effect system, to address Haskell's difficulties in reasoning about lazy evaluation and in using traditional data structures such as mutable arrays. He argues (p. 20) that "destructive update furnishes the programmer with two important and powerful tools ... a set of efficient array-like data structures for managing collections of objects, and ... the ability to broadcast a new value to all parts of a program with minimal burden on the programmer."
Robert Harper, one of the authors of Standard ML, has given his reasons for not using Haskell to teach introductory programming. Among these are the difficulty of reasoning about resource use with non-strict evaluation, that lazy evaluation complicates the definition of datatypes and inductive reasoning, and the "inferiority" of Haskell's (old) class system compared to ML's module system.
Haskell's build tool, Cabal
A cabal is a group of people who are united in some close design, usually to promote their private views or interests in an ideology, a state (polity), state, or another community, often by Wiktionary:intrigue, intrigue and usually without the kn ...
, has historically been criticized for poorly handling multiple versions of the same library, a problem known as "Cabal hell". The Stackage server and Stack build tool were made in response to these criticisms. Cabal itself has since addressed this problem by borrowing ideas from Nix, with the new approach becoming the default in 2019.
Related languages
Clean is a close, slightly older relative of Haskell. Its biggest deviation from Haskell is in the use of uniqueness types instead of monads for input/output
In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...
(I/O) and side effects.
A series of languages inspired by Haskell, but with different type systems, have been developed, including:
* Agda, a functional language with dependent types.
* Cayenne, with dependent types.
* Elm, a functional language to create web front-end apps, no support for user-defined or higher- kinded type classes or instances.
* Epigram
An epigram is a brief, interesting, memorable, sometimes surprising or satirical statement. The word derives from the Greek (, "inscription", from [], "to write on, to inscribe"). This literary device has been practiced for over two millennia ...
, a functional language with dependent types suitable for proving properties of programs.
* Idris, a general purpose functional language with dependent types, developed at the University of St Andrews
The University of St Andrews (, ; abbreviated as St And in post-nominals) is a public university in St Andrews, Scotland. It is the List of oldest universities in continuous operation, oldest of the four ancient universities of Scotland and, f ...
.
* PureScript transpiles to JavaScript.
* Ωmega, a strict language that allows introduction of new kinds, and programming at the type level.
Other related languages include:
* Curry, a functional/logic programming language based on Haskell.
Notable Haskell variants include:
* Generic Haskell, a version of Haskell with type system support for generic programming.
* Hume, a strict functional language for embedded system
An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...
s based on processes as stateless automata over a sort of tuples of one element mailbox channels where the state is kept by feedback into the mailboxes, and a mapping description from outputs to channels as box wiring, with a Haskell-like expression language and syntax.
Conferences and workshops
The Haskell community meets regularly for research and development activities. The main events are:
* International Conference on Functional Programming (ICFP)
* Haskell Symposium (formerly the Haskell Workshop)
* Haskell Implementors Workshop
* Commercial Users of Functional Programming (CUFP)
* ZuriHac, kind of Hackathon
A hackathon (also known as a hack day, hackfest, datathon or codefest; a portmanteau of '' hacking'' and ''marathon'') is an event where people engage in rapid and collaborative engineering over a relatively short period of time such as 24 or 48 h ...
held every year in Zurich
Zurich (; ) is the list of cities in Switzerland, largest city in Switzerland and the capital of the canton of Zurich. It is in north-central Switzerland, at the northwestern tip of Lake Zurich. , the municipality had 448,664 inhabitants. The ...
Starting in 2006, a series of organized ''hackathons'' has occurred, the Hac series, aimed at improving the programming language tools and libraries.
References
Bibliography
; Reports
*
*
; Textbooks
*
*
*
*
Real World Haskell
(full text).
*
*
full text
*
*
; Tutorials
*
*Learn You a Haskell for Great Good! - A community version (
learnyouahaskell.github.io
''. An up-to-date community maintained version of the renowned "Learn You a Haskell" (LYAH) guide.
* Assumes far less prior knowledge than official tutorial.
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Academic programming languages
Educational programming languages
Functional languages
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Pattern matching programming languages
Programming languages created in 1990
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Articles with example Haskell code