Editing Mercury (programming language) (section)

==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.

The language is designed using [[software engineering]] principles. Unlike the original implementations of Prolog, it has a separate [[compiler|compilation]] phase, rather than being directly interpreted. This allows a much wider range of errors to be detected before running a program. It features a strict [[Type system#Static type checking|static type]] and mode system<ref name=motivation/> and a module system.

By using information obtained at compile time (such as type and mode), programs written in Mercury typically perform significantly faster than equivalent programs written in Prolog.<ref name="benchmarks">[http://www.mercurylang.org/about/benchmarks.html The Mercury Project - Benchmarks]</ref><ref name="jlp">{{cite journal
 |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
 |volume= 29
 |issue= 1–3
 |pages= 17–64
 |publisher= Mercurylang.org
 |date= October–December 1996
 |url= http://www.mercurylang.org/documentation/papers.html#jlp
 |doi= 10.1016/S0743-1066(96)00068-4
 |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>!</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, it serves mainly as a way to call foreign language code. All impure code must be 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 ODASE has also been using Mercury to develop its Ontology-Centric software development platform, ODASE.<ref>[https://www.odase.io/ ODASE]</ref>