Mercury (programming language): Difference between revisions

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{{Short description|Functional logic programming language}}

{{For|Mercury Autocode|Autocode}}

{{Distinguish|Mercurial|Mercury (RemObjects BASIC programming language)}}

{{other uses|Mercury (disambiguation)}}

{{Infobox programming language

| name = Mercury

| logo = Mercury (programming language) logo.jpg

| paradigm = [[Logic programming|Logic]], [[Functional programming|functional]], [[Object-oriented programming|object-oriented]]{{citation needed|date=February 2024}}

| family = [[Prolog]], [[Haskell]]

| designer = Zoltan Somogyi

| developer = [[University of Melbourne]]

| released = {{Start date and age|1995|04|08}}

| latest release version = 14.01.1{{wikidata|property|preferred|references|edit|P348|P548=Q2804309}}

| latest release date = {{Start date and age|2014{{wikidata|09qualifier|08preferred|single|P348|P548=Q2804309|P577}}|df=yes}}

| typing = [[Strong and weak typing|Strongstrong]], [[Type system#Static type checking|static]], [[Polymorphism (computer science)|polymorphic]]

| scope = [[Scope (computer science)|lexical]]

| programming language = Mercury

| platform = [[IA-32]], [[x86-64]], [[ARM architecture family|ARM]], [[SPARC|Sparc64]]64, [[Java (software platform)|Java]], [[Common Language Infrastructure|CLI]], [[Open Telecom Platform|Erlang/OTP]]

| operating system = [[Cross-platform software|Cross-platform]]: [[Unix]], [[Linux]], [[macOS]], [[Oracle Solaris (operating system)|Solaris]], [[FreeBSD]], [[OpenBSD]], [[Microsoft Windows|Windows]], [[Android (operating system)|Android]]

| license = [[GNU General Public License|GPL]] compiler,<br />[[GNU Lesser General Public License|LGPL]] standard library

| file ext = .m

| file format =

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| implementations = Melbourne Mercury Compiler

| dialects =

| influenced by = [[Prolog]], [[Hope (programming language)|Hope]], [[Haskell (programming language)|Haskell]]

| influenced =

}}

'''Mercury''' is a [[functional logic programming]] language made for real-world uses. The first version was developed at the [[University of Melbourne]], Computer Science department, by Fergus Henderson, Thomas Conway, and Zoltan Somogyi, under Somogyi's supervision, and released on April 8, 1995.

Mercury is a purely [[Declarative programming|declarative]] [[logic programming]] language. It is related to both [[Prolog]] and [[Haskell (programming language)|Haskell]].<ref name="motivation">[http://www.mercurylang.org/about/motivation.html The Mercury Project - Motivation]</ref> It features a strong, static, polymorphic [[type system]], and a strong mode and determinism system.

The official implementation, the Melbourne Mercury Compiler, is available for most [[Unix]] and [[Unix-like]] platforms, including [[Linux]], [[macOS]], and for [[Microsoft Windows|Windows (32bits only)]].

== Overview ==

== Overview ==

Mercury is based on the logic programming language [[Prolog]]. It has the same syntax and the same basic concepts such as the [[SLD resolution|selective linear definite clause resolution]] (SLD) algorithm. It can be viewed as a pure subset of Prolog with strong types and modes. As such, it is often compared to its predecessor in features and run-time efficiency.

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|last= Somogyi

|first= Zoltan

|last2= Henderson |first2= Fergus |last3= Conway |first3= Thomas

|title= The execution algorithm of Mercury: an efficient purely declarative logic programming language

|journal= Journal of Logic Programming

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|pages= 17–64

|publisher= Mercurylang.org

|___location=

|date= October–December 1996

|url= http://www.mercurylang.org/documentation/papers.html#jlp

|doi= 10.1016/S0743-1066(96)00068-4

|id=

|access-date = 2008-08-30|citeseerx=10.1.1.46.9861}}</ref> Its authors claim that Mercury is the fastest logic language in the world, by a wide margin.<ref name="motivation"/>

Mercury is a purely [[Declarative programming|declarative]] language, unlike [[Prolog]], since it lacks ''extra-logical'' Prolog statements such as <code>cut!</code> (cut) and [[imperative programming|imperative]] [[input/output]] (I/O). This enables advanced [[static program analysis]] and [[program optimization]], including compile-time [[Garbage collection (computer science)|garbage collection]],<ref>{{cite thesis

|url=https://mercurylang.org/documentation/papers/CW2004_03_mazur.pdf

|title=Compile-time garbage collection for the declarative language Mercury

|first=Nancy |last=Mazur |date=May 2004 |publisher=Katholieke Universiteit Leuven}}</ref> but it can make certain programming constructs (such as a switch over a number of options, with a default{{Dubious|Examples_of_difficulties_introduced_by_declarativeness.3F|date=February 2009}}) harder to express. (While Mercury does allow impure functionality, thisit serves mainly as a way to call foreign language code. All impure code must be marked explicitly marked.) Operations which would typically be impure (such as [[input/output]]) are expressed using pure constructs in Mercury using [[Linear type system|linear types]], by threading a dummy ''world'' value through all relevant code.

Notable programs written in Mercury include the Mercury compiler and the [[Prince XML]] formatter. The Software company Mission Critical ITODASE has also been using Mercury since 2000 to develop enterprise applications and its Ontology-DrivenCentric software development platform, ODASE.<ref>[httphttps://www.missioncriticalitodase.comio/ Mission Critical ITODASE]</ref>

==Back-ends==

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===Production level===

* Low-level [[C (programming language)|C]] for [[GNU Compiler Collection]] (GCC), the original Mercury back-end

* High-level C

* [[Java (programming language)|Java]]

* [[C Sharp (programming language)|C#]]

*[[Erlang (programming language)|Erlang]]

===Past===

* [[Assembly language]] via the GCC back-end

* Aditi, a deductive database system also developed at the [[University of Melbourne]]. Mercury-0.12.2 is the last version to support Aditi.{{citation needed|date=January 2014}}

* [[Common Intermediate Language]] (CIL) for the [[.NET Framework]]

* [[Erlang (programming language)|Erlang]]

Mercury also features a foreign language interface, allowing code in other languages (depending on the chosen back-end) to be linked with Mercury code. The following foreign languages are possible:

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== Examples ==

[[Hello world program|Hello World]]:

<sourcesyntaxhighlight lang="prolog">

:- module hello.

:- interface.

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main(!IO) :-

io.write_string("Hello, World!\n", !IO).

</syntaxhighlight>

</source>

Calculating the 10th [[Fibonacci number]] (in the most obvious way):<ref name="tutorial">Adapted from [http://www.mercurylang.org/documentation/papers/book.pdf Ralph Becket's Mercury tutorial]</ref>

<sourcesyntaxhighlight lang="prolog">

:- module fib.

:- interface.

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io.nl(!IO).

% Could instead use io.format("fib(10) = %d\n", [i(fib(10))], !IO).

</syntaxhighlight>

</source>

<code>!IO</code> is a "state variable", which is [[syntactic sugar]] for a pair of variables which are assigned concrete names at compilation; for example, the above is desugared to something like:

<syntaxhighlight lang="prolog">

main(IO0, IO) :-

io.write_string("fib(10) = ", IO0, IO1),

io.write_int(fib(10), IO1, IO2),

io.nl(IO2, IO).

</syntaxhighlight>

==Release schedule==

The stable release naming scheme was 0.1 up to 0.13 for the first thirteen stable releases. In February 2010 the Mercury project decided to name each stable release by using the year and month of the release. For example 10.04 is for a release made in April 2010.

Releases are named according to the year and month of release. The current stable release is 14.01.1 (September 2014). Prior releases were numbered 0.12, 0.13, etc., and the time between stable releases can be as long as 3 years.

There is often also a periodic snapshot of the development system ''release of the day'' (ROTD) consisting of the latest features and bug fixes added to the last stable release.

==IDE and editor support==

* Developers providesprovide support for [[Vim (text editor)|Vim]]

* Flycheck library for [[Emacs]]

* A plugin is available for the [[Eclipse (software)|Eclipse IDE]]

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* {{Official website|www.mercurylang.org}}

<br />

{{DEFAULTSORT:Mercury (programming language)}}

[[Category:Programming languages]]

[[Category:Cross-platform free software]]

[[Category:Functional languages]]

[[Category:Functional logic programming languages]]

[[Category:Logic programming languages]]

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[[Category:Programming languages created in 1995]]

[[Category:ProgrammingStatically typed programming languages]]