Editing Prolog (section)

== Modules ==
For [[Programming in the large and programming in the small#Programming in the large|programming in the large]], Prolog provides a [[modular programming|module system]], which is in the ISO Standard.<ref>ISO/IEC 13211-2: Modules.</ref>
However, while most Prolog systems support structuring the code into modules, virtually no implementation adheres to the modules part of the ISO standard. Instead, most [[Comparison of Prolog implementations|Prolog systems]] have decided to support as ''de-facto'' module standard the [[Quintus Prolog|Quintus]]/[[SICStus]] module system. However, further convenience predicates concerning modules are provided by some implementations only and often have subtle differences in their semantics.<ref name="auto">{{citation |author=Philipp Körner |author2=Michael Leuschel |author3=João Barbosa |author4=Vítor Santos Costa |author5=Verónica Dahl |author6=Manuel V. Hermenegildo |author7=Jose F. Morales |author8=Jan Wielemaker |author9=Daniel Diaz |author10=Salvador Abreu |author11=Giovanni Ciatto |title=Fifty Years of Prolog and Beyond |date=November 2022 |journal=Theory and Practice of Logic Programming|volume=22|issue=6 |pages=776–858 |doi=10.1017/S1471068422000102 |doi-access=free|hdl=10174/33387 |hdl-access=free }}</ref>

Some systems chose to implement module concepts as source-to-source compilation into base ISO Prolog, as is the case of [[Logtalk]].<ref name="cs.kuleuven.ac.be">{{citation|first=Paulo|last=Moura|title=Logtalk|journal=Association of Logic Programming|volume=17|issue=3|date=August 2004|url=http://www.cs.kuleuven.ac.be/~dtai/projects/ALP/newsletter/aug04/nav/print/all.html#logtalk|access-date=2010-02-16|archive-date=2010-04-12|archive-url=https://web.archive.org/web/20100412151301/http://www.cs.kuleuven.ac.be/~dtai/projects/ALP/newsletter/aug04/nav/print/all.html#logtalk|url-status=dead}}</ref> GNU Prolog initially diverted from ISO modules, opting instead for [[Contextual Logic Programming]], in which unit (module) loading and unloading can be made dynamically.<ref>{{citation|last1=Abreu|last2=Nogueira|year=2005|journal=Lecture Notes in Artificia Intelligence|volume=4369|title=Using a Logic Programming Language with Persistence and Contexts}}</ref>  [[Ciao (programming language)|Ciao]] designed a strict module system that, while being basically compatible with the ''de-facto'' standard used by other Prolog systems, is amenable to precise static analysis, supports term hiding, and facilitates programming in the large.<ref>{{citation|last1=Cabeza|last2=Hermenegildo|title=A new module system for Prolog|series=Lecture Notes in Computer Science|volume=1861|year=2000}}</ref>  [[XSB]] takes a different approach and offers an ''atom-based'' module system.<ref>{{citation|last1=Sagonas|last2=Swift|last3=Warren|year=1994|title=XSB as an efficient deductive database engine |journal=SIGMOD}}</ref> The latter two Prolog systems allow controlling the ''visibility of terms'' in addition to that of predicates.<ref name="auto"/>