View source for PureScript

{{Short description|Strongly-typed language that compiles to JavaScript}}
{{Infobox programming language
| name = PureScript
| logo = PureScript Logo.png
| paradigm = [[Functional programming|Functional]]
| year = 2013
| latest release version = 0.15.12
| latest release date = {{Start date and age|2023|10|7}}
| influenced_by = [[Haskell (programming language)|Haskell]], [[JavaScript]]
| typing = [[Type inference|Inferred]], static, strong
| designer = Phil Freeman
| website = {{official URL}}
| license = BSD<ref name=license>{{cite web|url=https://github.com/purescript/purescript/blob/master/LICENSE|title=purescript/purescript|website=GitHub|date=3 June 2022 }}</ref>
| file_ext = .purs
}}

'''PureScript''' is a strongly-typed, [[Purely functional programming|purely-functional]] [[Programming language|programming language]] that [[Source-to-source compiler|transpile]]s to [[JavaScript]],<ref>{{Cite web | url=https://github.com/purescript/purescript | title=PureScript to JavaScript transpiler | website=[[GitHub]] | access-date=2023-01-22}}</ref> [[C++11]],<ref>{{Cite web | url=https://github.com/andyarvanitis/purescript-native/tree/cpp | title=PureScript to C++11 transpiler | website=[[GitHub]] | access-date=2023-01-22}}</ref> [[Erlang (programming language)|Erlang]],<ref>{{Citation |title=purerl - the PureScript Erlang backend |date=2023-09-04 |url=https://github.com/purerl/purerl |access-date=2023-09-05 |publisher=purerl}}</ref> and [[Go (programming language)|Go]].<ref>{{Cite web | url=https://github.com/andyarvanitis/purescript-native | title=PureScript to Go transpiler | website=[[GitHub]] | access-date=2023-01-22}}</ref> It can be used to develop web applications, server side apps, and also desktop applications with use of [[Software:Electron (software framework)|Electron]] or via C++11 and Go compilers with suitable libraries. Its syntax is mostly comparable to that of [[Haskell (programming language)|Haskell]]. In addition, it introduces [[Row polymorphism|row polymorphism]] and [[Software:Hugs (interpreter)|extensible records]].<ref>{{Cite web|url=https://purescript.org/|title=PureScript|website=purescript.org|access-date=2019-03-14}}</ref> Also, contrary to Haskell, the PureScript language is defined as having a [[Evaluation strategy#Strict evaluation|strict evaluation strategy]],<ref>{{Citation |title=purescript/documentation |date=2023-02-19 |url=https://github.com/purescript/documentation/blob/ddc83562aa1de9d4e2c1067c71bf3d4e3b77b84d/language/Differences-from-Haskell.md |publisher=PureScript |access-date=2023-02-20}}</ref> although there are non-conforming back ends which implement a [[Evaluation strategy#Non-strict evaluation|lazy evaluation strategy]].<ref>{{Citation |title=Alternative backends |date=2023-02-19 |url=https://github.com/purescript/documentation/blob/ddc83562aa1de9d4e2c1067c71bf3d4e3b77b84d/ecosystem/Alternate-backends.md |publisher=PureScript |access-date=2023-02-20}}</ref>

== History ==
PureScript was initially designed by Phil Freeman in 2013. He started to work on PureScript since he wasn't satisfied by other attempts to transpile Haskell to JavaScript (e.g. using Fay, Haste, or GHCJS).<ref>{{Cite web|url=https://leanpub.com/purescript/read#leanpub-auto-about-the-author|title=Read PureScript by Example {{!}} Leanpub|website=leanpub.com|access-date=2019-03-14}}</ref>

Since then it has been picked up by the community and is developed on [[GitHub]]. Additional core tools developed by the community include the dedicated build tool "Pulp",<ref>{{Citation|title=A build tool for PureScript projects|date=2019-03-08|url=https://github.com/purescript-contrib/pulp|publisher=PureScript Contrib|access-date=2019-03-14}}</ref> the documentation directory "Pursuit",<ref>{{Cite web|url=https://pursuit.purescript.org/|title=Pursuit|website=pursuit.purescript.org|access-date=2019-03-14}}</ref> and the package manager "Spago"<ref>{{Citation|title=🍝 PureScript package manager and build tool powered by Dhall and package-sets: spacchetti/spago|date=2019-03-14|url=https://github.com/spacchetti/spago|publisher=spacchetti|access-date=2019-03-14}}</ref>

== Features ==
PureScript features [[Eager evaluation|strict evaluation]], persistent data structures and [[Type inference|type inference]]. The PureScript type system shares many features with those of similar functional languages like [[Haskell (programming language)|Haskell]]: [[Algebraic data type|algebraic data type]]s and [[Pattern matching|pattern matching]], higher kinded types, [[Type class|type class]]es and [[Type class#Functional dependencies|functional dependencies]], and higher-rank polymorphism. PureScript's type system adds support for [[Row polymorphism|row polymorphism]] and extensible records.<ref>{{Citation|title=Documentation for the PureScript language, compiler, and tools.: purescript/documentation|date=2019-03-14|url=https://github.com/purescript/documentation|publisher=PureScript|access-date=2019-03-14}}</ref> However, PureScript lacks support for some of the more advanced features of Haskell like [[Generalized algebraic data type|GADTs]] and [[Type family|type families]].

The PureScript transpilers attempt to produce readable code, where possible. Through a simple [[Foreign function interface|FFI interface]], it also allows the reuse of existing JavaScript<ref>{{Cite web | title=The Foreign Function Interface | date=2015-07-15 | url=https://github.com/purescript/documentation/blob/master/guides/FFI.md | publisher=PureScript | access-date=2023-01-22}}</ref>/C++11<ref>{{Cite web | title=FFI | date=2019-07-26 | url=https://github.com/andyarvanitis/purescript-native/wiki/FFI | publisher=PureScript | access-date=2023-01-22}}</ref><ref>{{Citation | title=C++ foreign export implementations for the standard library | date=2019-07-26 | url=https://github.com/andyarvanitis/purescript-native-cpp-ffi | publisher=PureScript | access-date=2023-01-22}}</ref>/Go<ref>{{Cite web | title=Go foreign export implementations for the standard library | date=2020-12-13 | url=https://github.com/andyarvanitis/purescript-native-go-ffi | publisher=PureScript | access-date=2023-01-22}}</ref> code.

PureScript supports incremental compilation, and the transpiler to JavaScript distribution includes support for building [[Software:Source code editor|source code editor]] plugins for iterative development.<ref>{{Citation|title=purs ide: Editor and tooling support for the PureScript programming language|date=2019-04-21|url=https://github.com/purescript/purescript/tree/dfbd19da85c92d82ed4c3184f950f74da5332e3f/psc-ide|access-date=2019-04-21}}</ref> Editor plugins exist for many popular text editors, including [[Software:Vim (text editor)|Vim]], [[Software:Emacs|Emacs]], [[Software:Sublime Text|Sublime Text]], [[Software:Atom (text editor)|Atom]] and [[Software:Visual Studio Code|Visual Studio Code]].

PureScript supports type-driven development via its typed holes feature,<ref>{{Citation|title=Implementing type directed search for PureScript|date=2016-10-27}}</ref> in which a program can be constructed with missing subexpressions. The JavaScript transpiler will subsequently attempt to infer the types of the missing subexpressions, and report those types to the user. This feature has inspired similar work in the [[Software:Glasgow Haskell Compiler|GHC]] [[Haskell (programming language)|Haskell]] compiler.<ref>{{Citation|title=Suggesting Valid Hole Fits for Typed-Holes (Experience Report)|date=2018-09-27|url=https://dl.acm.org/citation.cfm?id=3242760|author=Matthías Páll Gissurarson|journal=ACM SIGPLAN Notices |volume=53 |issue=7 |pages=179–185 |doi=10.1145/3299711.3242760 |s2cid=218480974 }}</ref>

== Examples ==
Here is a minimal "Hello world" program in PureScript:

<source lang="haskell" line="1">
module Main where

import Effect.Console (log)

main = log "Hello World!"
</source>

Here, the type of the program is inferred and checked by the PureScript transpiler. A more verbose version of the same program might include explicit type annotations:

<source lang="haskell" line="1">
module Main where

import Prelude

import Effect (Effect)
import Effect.Console (log)

main :: Effect Unit
main = log "Hello World!"
</source>

== See also ==
* {{annotated link|Elm (programming language)}}
* {{annotated link|Reason (programming language)}}
* {{annotated link|JS++}}
* {{annotated link|TypeScript}}

== References ==
{{Reflist|2}}

== External links ==
* [https://app.qvault.io/playground/purescript PureScript Playground]

{{Programming languages}}

[[Category:Functional languages]]
[[Category:Pattern matching programming languages]]
[[Category:Statically typed programming languages]]

{{Sourceattribution|PureScript}}