Flix (programming language): Difference between revisions

Revision as of 09:07, 16 June 2022

Revision as of 16:58, 27 July 2022

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| typing = [[Hindley-Milner|inferred]], [[Static typing|static]], [[Strong and weak typing|strong]], [[structural typing|structural]]

| platform = [[Java virtual machine|JVM]]

| license = [[Apache License 2.0]].<ref name="license-github">{{cite web |url=https://github.com/flix/flix/blob/master/LICENSE.md|title=Apache License 2.0|date=27 July 2022 |via=[[GitHub]]}}</ref>

| website = {{URL|https://flix.dev/}}

| influenced_by = [[F Sharp (programming language)|F#]], [[Go (programming language)|Go]], [[Haskell (programming language)|Haskell]], [[OCaml]], [[Scala (programming language)|Scala]]

| file_ext = .flix

}}

'''Flix''' is a [[functional programming|functional]], [[imperative programming|imperative]], and [[logic programming|logic]] [[programming language]] developed at [[Aarhus University]], with funding from the [[Danish Council for Independent Research|Independent Research Fund Denmark]],<ref>{{cite web |title=Forskningsprojekter |url=https://dff.dk/forskningsprojekter?SearchableText=functional+and+declarative+logic+programming&period%3Alist=all&instrument%3Alist=all&filed_method%3Alist=all |website=Danmarks Frie Forskningsfond |language=da}}</ref> and by a community of [[open source]] contributors.<ref>{{cite web |title=Flix Authors |url=https://github.com/flix/flix/blob/master/AUTHORS.md |website=GitHub |date=27 July 2022 |language=en}}</ref> The Flix language supports [[algebraic data types]], [[pattern matching]], [[parametric polymorphism]], [[currying]], [[higher-order functions]], [[extensible records]],<ref>{{cite journal |last1=Leijen |first1=Daan |title=Extensible records with scoped labels |journal=Trends in Functional Programming}}</ref> [[Communicating sequential processes|channel and process-based concurrency]], and [[tail call elimination]]. Two notable features of Flix are its type and effect system<ref name="oopsla2020a">{{cite journal |last1=Madsen |first1=Magnus |last2=van de Pol |first2=Jaco |title=Polymorphic Types and Effects with Boolean Unification |journal=Proceedings of the ACM on Programming Languages |date=13 November 2020 |volume=4 |issue=OOPSLA |pages=1–29 |doi=10.1145/3428222|s2cid=227044242 |doi-access=free }}</ref> and its support for first-class Datalog constraints.<ref name="oopsla2020b">{{cite journal |last1=Madsen |first1=Magnus |last2=Lhoták |first2=Ondřej |title=Fixpoints for the Masses: Programming with First-class Datalog Constraints |journal=Proceedings of the ACM on Programming Languages |date=13 November 2020 |volume=4 |issue=OOPSLA |pages=125:1–125:28 |doi=10.1145/3428193|s2cid=227107960 |doi-access=free }}</ref>

The Flix type and effect system supports [[Hindley–Milner type system|Hindley-Milner]]-style [[type inference]]. The system separates pure and impure code: if an expression is typed as pure then it cannot produce an effect at run-time. Higher-order functions can enforce that they are given pure (or impure) function arguments. The type and effect system supports [[effect polymorphism]]<ref>{{cite journal |last1=Lucassen |first1=J. M. |last2=Gifford |first2=D. K. |title=Polymorphic effect systems |journal=Proceedings of the 15th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages - POPL '88 |date=1988 |pages=47–57 |doi=10.1145/73560.73564|isbn=0897912527 |s2cid=13015611 }}</ref><ref>{{cite journal |last1=Leijen |first1=Daan |title=Koka: Programming with Row Polymorphic Effect Types |journal=Electronic Proceedings in Theoretical Computer Science |date=5 June 2014 |volume=153 |pages=100–126 |doi=10.4204/EPTCS.153.8|arxiv=1406.2061 |s2cid=14902937 }}</ref> which means that the effect of a higher-order function may depend on the effect(s) of its argument(s).

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=== Polymorphic effects ===

The Flix type and effect system separates pure and impure expressions.<ref name="oopsla2020a"/><ref>{{cite web |title=Programming Flix - Effects |url=https://doc.flix.dev/effects/ |website=flix.dev}}</ref><ref>{{cite web|title=Rust Internals - Flix Polymorphic Effects|date=15 November 2020 |url=https://internals.rust-lang.org/t/flix-polymorphic-effects/13395}}</ref> A pure expression is guaranteed to be [[Referential transparency|referentially transparent]]. A pure function always returns the same value when given the same argument(s) and cannot have any (observable) side-effects.

For example, the following expression is of type <code>Int</code> and is <code>Pure</code>: