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44-405: Haskell ( / ˈ h æ s k əl / ) is a general-purpose , statically-typed , purely functional programming language with type inference and lazy evaluation . Designed for teaching, research, and industrial applications, Haskell has pioneered several programming language features such as type classes , which enable type-safe operator overloading , and monadic input/output (IO). It

88-794: A BSD license . GHC originally begun in 1989 as a prototype, written in Lazy ML (LML) by Kevin Hammond at the University of Glasgow . Later that year, the prototype was completely rewritten in Haskell, except for its parser , by Cordelia Hall, Will Partain, and Simon Peyton Jones. Its first beta release was on 1 April 1991. Later releases added a strictness analyzer and language extensions such as monadic I/O , mutable arrays, unboxed data types, concurrent and parallel programming models (such as software transactional memory and data parallelism ) and

132-584: A profiler . Peyton Jones, and Marlow, later moved to Microsoft Research in Cambridge , where they continued to be primarily responsible for developing GHC. GHC also contains code from more than three hundred other contributors. From 2009 to about 2014, third-party contributions to GHC were funded by the Industrial Haskell Group. Since early releases the official website has referred to GHC as The Glasgow Haskell Compiler , whereas in

176-437: A general purpose programming language.  For example, COBOL , Fortran , and Lisp were created as DSLs (for business processing, numeric computation, and symbolic processing), but became GPL's over time. Inversely, a language may be designed for general use but only applied in a specific area in practice. A programming language that is well suited for a problem, whether it be general-purpose language or DSL, should minimize

220-773: A general-purpose language with an appropriate library of data types and functions for the domain may be used instead. While DSLs are usually smaller than GPL in that they offer a smaller range of notations of abstractions, some DSLs actually contain an entire GPL as a sublanguage. In these instances, the DSLs are able to offer domain-specific expressive power along with the expressive power of GPL. General Purpose programming languages are all Turing complete , meaning that they can theoretically solve any computational problem. Domain-specific languages are often similarly Turing complete but are not exclusively so. General-purpose programming languages are more commonly used by programmers. According to

264-602: A much more sophisticated build system, heavily inspired by Nix , which became the default with version 3.0. 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 (I/O) and side effects. A series of languages inspired by Haskell, but with different type systems, have been developed, including: Other related languages include: Notable Haskell variants include: The Haskell community meets regularly for research and development activities. The main events are: Starting in 2006,

308-607: A result, though it was first used by its creators to rewrite the kernel of the Unix operating system, it was easily adapted for use in application development, embedded systems (e.g., microprocessor programming), video games (e.g., Doom ), and so on. Today, C remains one of the most popular and widely-used programming languages. Conceived as an extension to C, C++ introduced object-oriented features, as well as other conveniences like references, operator overloading, and default arguments. Like C, C++'s generality allowed it to be used in

352-830: A series of organized hackathons has occurred, the Hac series, aimed at improving the programming language tools and libraries. General-purpose programming language Early programming languages were designed for scientific computing (numerical calculations) or commercial data processing, as was computer hardware. Scientific languages such as Fortran and Algol supported floating-point calculations and multidimensional arrays, while business languages such as COBOL supported fixed-field file formats and data records . Much less widely used were specialized languages such as IPL-V and LISP for symbolic list processing ; COMIT for string manipulation; APT for numerically controlled machines . Systems programming requiring pointer manipulation

396-479: A set of rules included in GHC's standard libraries that performs foldr/build fusion ), unfolding (called " inlining " in more traditional compilers), let-floating , an analysis that determines which function arguments can be unboxed, constructed product result analysis , specialization of overloaded functions, and a set of simpler local transformations such as constant folding and beta reduction . The back end of

440-465: A study, C , Python , and Java were the most commonly used programming languages in 2021.  One argument in favor of using general-purpose programming languages over domain-specific languages is that more people will be familiar with these languages, overcoming the need to learn a new language. Additionally, for many tasks (e.g., statistical analysis, machine learning, etc.) there are libraries that are extensively tested and optimized. Theoretically,

484-459: A wide range of areas. While its C++'s core area of application is in systems programming (because of C++'s ability to grant access to low-level architecture), it has been used extensively to build desktop applications, video games, databases, financial systems, and much more. Major software and finance companies, such as Microsoft , Apple , Bloomberg , and Morgan Stanley , still widely use C++ in their internal and external applications. Python

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528-452: Is a purely functional programming language, which means that functions generally have no side effects . A distinct construct exists to represent side effects, orthogonal 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

572-410: Is a native or machine code compiler for the functional programming language Haskell . It provides a cross-platform software environment for writing and testing Haskell code and supports many extensions, libraries , and optimisations that streamline the process of generating and executing code. GHC is the most commonly used Haskell compiler. It is free and open-source software released under

616-610: Is an incremental update to the language, mostly incorporating several well-used and uncontroversial features previously enabled via compiler-specific flags. 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. Haskell features lazy evaluation , lambda expressions , pattern matching , list comprehension , type classes and type polymorphism . It

660-455: Is designed to preserve as much information about the source language as possible until after type inference is complete, toward the goal of providing clear error messages to users. After type checking, the Haskell code is desugared into a typed intermediate language known as "Core" (based on System F , extended with let and case expressions). Core has been extended to support generalized algebraic datatypes in its type system , and

704-622: Is named after logician Haskell Curry . Haskell's main implementation is the Glasgow Haskell Compiler (GHC). Haskell's semantics 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

748-485: Is now based on an extension to System F known as System F C . In the tradition of type-directed compiling, GHC's simplifier, or "middle end", where most of the optimizations implemented in GHC are performed, is structured as a series of source-to-source transformations on Core code. The analyses and transformations performed in this compiler stage include demand analysis (a generalization of strictness analysis ), application of user-defined rewrite rules (including

792-558: 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 and software transactional memory . They are defined as ordinary datatypes, but Haskell provides some syntactic sugar for their use. Haskell has an open, published specification, and multiple implementations exist . Its main implementation,

836-489: Is used in academia and industry. As of May 2021, Haskell was the 28th most popular programming language by Google searches for tutorials, and made up less than 1% of active users on the GitHub source code repository. 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

880-488: 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). In late 1997, the series culminated in Haskell 98 , intended to specify a stable, minimal, portable version of

924-527: The Glasgow Haskell Compiler (GHC) implementation representing the current de facto standard. 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

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968-426: The Glasgow Haskell Compiler (GHC), is both an interpreter and native-code compiler that runs on most platforms. GHC is noted for its rich type system incorporating recent innovations such as generalized algebraic data types and type families. The Computer Language Benchmarks Game also highlights its high-performance implementation of concurrency and parallelism . An active, growing community exists around

1012-456: 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 over lists, where the first element is taken as the pivot: All listed implementations are distributed under open source licenses . Implementations that fully or nearly comply with

1056-451: The 1960s: GPSS and Simula for discrete event simulation; MAD , BASIC , Logo , and Pascal for teaching programming; C for systems programming; JOSS and APL\360 for interactive programming. The distinction between general-purpose programming languages and domain-specific programming languages is not always clear. A programming language may be created for a specific task, but used beyond that original domain and thus be considered

1100-580: The Haskell 98 standard include: Implementations no longer actively maintained include: Implementations not fully Haskell 98 compliant, and using a variant Haskell language, include: Notable web frameworks written for Haskell include: 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

1144-419: The compiler transforms Core code into an internal representation of C--, via an intermediate language STG (short for "Spineless Tagless G-machine"). The C-- code can then take one of three routes: it is either printed as C code for compilation with GCC , converted directly into native machine code (the traditional " code generation " phase), or converted to LLVM IR for compilation with LLVM. In all three cases,

1188-511: 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 , 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 now has

1232-595: The error messages researchers from Utrecht University developed an advanced interpreter called Helium , 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

1276-431: The executable version command it is identified as The Glorious Glasgow Haskell Compilation System . This has been reflected in the documentation. Initially, it had the internal name of The Glamorous Glasgow Haskell Compiler . GHC is written in Haskell , but the runtime system for Haskell, essential to run programs, is written in C and C-- . GHC's front end , incorporating the lexer , parser and typechecker ,

1320-496: The language and an accompanying standard library 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

1364-535: The language specification, or they redefine existing constructs. As such, each extension may not be supported by all Haskell implementations. There is an ongoing effort to describe extensions and select those which will be included in future versions of the language specification. The extensions supported by the Glasgow Haskell Compiler include: An expressive static type system is one of the major defining features of Haskell. Accordingly, much of

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1408-511: The language, and more than 5,400 third-party open-source libraries and tools are available in the online package repository Hackage . A "Hello, World!" program in Haskell (only the last line is strictly necessary): The factorial 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): Using Haskell's Fixed-point combinator allows this function to be written without any explicit recursion. As

1452-438: The level of detail required while still being expressive enough in the problem domain. As the name suggests, general-purpose language is "general" in that it cannot provide support for domain-specific notation while DSLs can be designed in diverse problem domains to handle this problem. General-purpose languages are preferred to DSLs when an application domain is not well understood enough to warrant its own language. In this case,

1496-446: 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

1540-624: The presence of these libraries should bridge the gap between general-purpose and domain-specific languages. An empirical study in 2010 sought to measure problem-solving and productivity between GPLs and DSLs by giving users problems who were familiar with the GPL ( C# ) and unfamiliar with the DSL ( XAML ). Ultimately, users of this specific domain-specific language performed better by a factor of 15%, even though they were more familiar with GPL, warranting further research. The predecessor to C , B ,

1584-404: 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

1628-455: The resultant native code is finally linked against the GHC runtime system to produce an executable. GHC complies with the language standards, both Haskell 98 and Haskell 2010 . It also supports many optional extensions to the Haskell standard: for example, the software transactional memory (STM) library, which allows for Composable Memory Transactions . Many extensions to Haskell have been proposed. These provide features not described in

1672-537: Was conceived as a language that emphasized code readability and extensibility. The former allowed non-software engineers to easily learn and write computer programs, while the latter allowed domain specialists to easily create libraries suited to their own use cases. For these reasons, Python has been used across a wide range of domains. Below are some of the areas where Python is used: The following are some general-purpose programming languages: Glasgow Haskell Compiler The Glasgow Haskell Compiler ( GHC )

1716-575: 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 (IO) were handled by both streams based and continuation based mechanisms which were widely considered unsatisfactory. In version 1.3, monadic IO

1760-467: Was developed largely for a specific purpose: systems programming . By contrast, C has found use in a variety of computational domains, such as operating systems , device drivers , application software , and embedded systems . C is suitable for use in a variety of areas because of its generality. It provides economy of expression, flow control, data structures, and a rich set of operators, but does not constrain its users to use it in any one context. As

1804-464: 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

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1848-510: Was the most widely used, but it was proprietary software . At the conference on Functional Programming Languages and Computer Architecture (FPCA '87) in Portland, Oregon , there was a strong consensus that a committee be formed to define an open standard 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

1892-406: Was typically done in assembly language , though JOVIAL was used for some military applications. IBM 's System/360 , announced in 1964, was designed as a unified hardware architecture supporting both scientific and commercial applications, and IBM developed PL/I for it as a single, general-purpose language that supported scientific, commercial, and systems programming. Indeed, a subset of PL/I

1936-475: Was used as the standard systems programming language for the Multics operating system. Since PL/I, the distinction between scientific and commercial programming languages has diminished, with most languages supporting the basic features required by both, and much of the special file format handling delegated to specialized database management systems . Many specialized languages were also developed starting in

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