Editing Colon (punctuation) (section)

==Computing==
The character was on early typewriters and therefore appeared in most text encodings, such as [[Baudot code]] and [[EBCDIC]]. It was placed at code 58 in [[ASCII]] and from there inherited into Unicode. Unicode also defines several related characters:
*{{unichar|003A}}
*{{unichar|02D0}}, used in [[International Phonetic Alphabet|IPA]].<ref>{{cite web |title=The International Phonetic Alphabet |url=http://weston.ruter.net/projects/ipa-chart/view/ |work=Weston Ruter |access-date=27 October 2011 |year=2005 |archive-date=29 July 2012 |url-status=live |archive-url=https://archive.today/20120729122639/http://westonruter.github.com/ipa-chart/}}</ref>
*{{unichar|10781}}, IPA modifier-letter.<ref name="L220252">{{cite web |title=L2/20-252R: Unicode request for IPA modifier-letters (a), pulmonic |url=https://www.unicode.org/L2/L2020/20252r-mod-ipa-a.pdf |date=2020-11-08 |last1=Miller |first1=Kirk |last2=Ashby |first2=Michael |access-date=2022-09-21 |archive-date=2021-07-30 |archive-url=https://web.archive.org/web/20210730010133/https://www.unicode.org/L2/L2020/20252r-mod-ipa-a.pdf |url-status=live}}</ref>
*{{unichar|02D1}}, used in IPA.
*{{unichar|10782}}, IPA modifier-letter.<ref name="L220252"/>
*{{unichar|02F8}}, used by [[Uralic Phonetic Alphabet]].<ref>{{cite web |url=https://www.unicode.org/L2/L2002/02141-n2419-uralic-phonetic.pdf |title=L2/02-141: Uralic Phonetic Alphabet characters for the UCS |date=20 March 2002 |first1=Michael |last1=Everson |display-authors=etal |archive-date=19 February 2018 |url-status=live |archive-url=https://web.archive.org/web/20180219081033/https://www.unicode.org/L2/L2002/02141-n2419-uralic-phonetic.pdf}}</ref>
*{{unichar|05C3}}, compatible with right-to-left text.
*{{unichar|2236}}, for mathematical usage.
*{{unichar|2254}}, for use in pretty-printing programming languages.
*{{unichar|2255}}<ref>{{cite web |url=https://www.unicode.org/L2/L2000/00119-math.pdf |title=L2/00-119: Encoding Additional Mathematical Symbols in Unicode |last1=Whistler |first1=Ken |last2=Freytag |first2=Asmus |date=19 April 2000 |archive-date=19 February 2018 |url-status=live |archive-url=https://web.archive.org/web/20180219085257/https://www.unicode.org/L2/L2000/00119-math.pdf}}</ref>
*{{unichar|2360}}
*{{unichar|2982}}
*{{unichar|2A74}}
*{{unichar|205D|nlink=}}
*{{unichar|2AF6}}
*{{unichar|A789}}, see [[Colon (letter)]]. (This character is also sometimes used in [[Microsoft Windows|Windows]] [[filename]]s as it is identical to the colon in the [[Segoe UI]] font used for filenames. The colon itself is not permitted as it is a [[reserved character]].)
*{{unichar|FE13}}, compatibility character for the Chinese Standard [[GB 18030]].
*{{unichar|FF1A}}, for compatibility with [[halfwidth and fullwidth forms|halfwidth and fullwidth fonts]].
*{{unichar|FE55}}, compatibility character for the Chinese National Standard [[CNS 11643]].

===Programming languages===
{{See also|Semicolon#Computing usage}}

Many programming languages, most notably [[ALGOL]], [[Pascal (programming language)|Pascal]] and [[Ada (programming language)|Ada]], use a colon and equals sign {{code|1=:=}} as the [[assignment (computer science)|assignment operator]], to distinguish it from a single equals {{code|1==}} which is an equality test ([[C (programming language)|C]] instead uses a single equals as assignment, and a double equals {{code|1===}} as the equality test).<ref>{{cite web |url=https://wiki.freepascal.org/Becomes |title=Becomes |website=Free Pascal and Lazarus Wiki |date=4 February 2021 |archive-date=2 March 2022 |archive-url=https://web.archive.org/web/20220302024707/https://wiki.freepascal.org/Becomes |url-status=live}}</ref><ref>{{cite web |url=http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-5-2.html |title=Ada Reference Manual – 5.2 Assignment Statements |publisher=Ada Conformity Assessment Authority |year=2012 |archive-date=20 May 2020 |archive-url=https://archive.today/20200520204221/http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-5-2.html |url-status=live}}</ref>

Many languages including [[C (programming language)|C]] and [[Java (programming language)|Java]] use the colon to indicate the text before it is a [[label (computer science)|label]], such as a target for a [[goto]] or an introduction to a case in a [[switch statement]].<ref name='c99'>{{cite web |author=ISO/IEC JTC1/SC22/WG14 |date=7 September 2007 |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf |title=ISO/IEC 9899:TC3 – Programming languages – C |archive-date=16 April 2020 |archive-url=https://archive.today/20200416164053/http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf |url-status=live}}</ref>{{rp|p=131}}<ref>{{cite web |url=https://docs.oracle.com/javase/specs/jls/se18/html/jls-14.html |title=The Java Language Specification – Chapter 14. Blocks, Statements, and Patterns |website=Oracle Help Center |date=23 February 2022 |publisher=Oracle |archive-date=8 June 2022 |archive-url=https://web.archive.org/web/20220608143908/https://docs.oracle.com/javase/specs/jls/se18/html/jls-14.html |url-status=live}}</ref> In a related use, [[Python (programming language)|Python]] uses a colon to separate a control statement (the ''clause header'') from the block of statements it controls (the ''suite''):<ref>{{cite web |title=The Python Language Reference – 8. Compound statements |date=22 January 2016 |publisher=Python Software Foundation |url=https://docs.python.org/3/reference/compound_stmts.html |url-status=live |archive-url=https://archive.today/20160126080617/https://docs.python.org/3/reference/compound_stmts.html |archive-date=26 January 2016}}</ref>

<syntaxhighlight lang="python">
if test(x):
    print("test(x) is true!")
else:
    print("test(x) is not true...")
</syntaxhighlight>

In many languages, including [[JavaScript]], colons are used to define [[name–value pair]]s in a [[JSON|dictionary]] or [[Object (computer science)|object]].<ref>{{cite book |author=ECMA TC39 |title=ECMA-262 |edition=13th |publisher=Ecma International |date=June 2022 |url=https://www.ecma-international.org/wp-content/uploads/ECMA-262_13th_edition_june_2022.pdf |archive-date=4 July 2022 |url-status=live |archive-url=https://web.archive.org/web/20220704012713/https://www.ecma-international.org/wp-content/uploads/ECMA-262_13th_edition_june_2022.pdf}}</ref>{{rp|pp=96–100}} This is also used by data formats such as [[JSON]].{{Ref RFC|8259}} Some other languages use an equals sign.

<syntaxhighlight lang="javascript">
var obj = {
    name: "Charles",
    age: 18,
}
</syntaxhighlight>

The colon is used as part of the [[?:]] conditional operator in C and many other languages.<ref name='c99'/>{{rp|p=90}}

[[C++]] uses a double colon as the [[scope resolution operator]], and [[class member function|class member access]].<ref>{{cite web |url=https://en.cppreference.com/w/cpp/language/identifiers |title=Identifiers |website=C++ Reference |date=16 June 2022 |archive-date=22 July 2022 |archive-url=https://web.archive.org/web/20220722004426/https://en.cppreference.com/w/cpp/language/identifiers |url-status=bot: unknown |access-date=28 July 2022}}</ref> Most other languages use a period but C++ had to use this for compatibility with C. Another language using colons for scope resolution is [[Erlang (programming language)|Erlang]], which uses a single colon.<ref>{{cite web |url=https://www.erlang.org/doc/reference_manual/expressions.html |title=Erlang Reference Manual – Expressions |website=Erlang |date=15 July 2022 |publisher=Ericsson |archive-date=21 July 2022 |archive-url=https://web.archive.org/web/20220721195015/https://www.erlang.org/doc/reference_manual/expressions.html |url-status=bot: unknown |access-date=28 July 2022}}</ref>

In [[BASIC]], it is used as a separator between the statements or instructions in a single line. Most other languages use a semicolon, but BASIC had used semicolon to separate items in print statements.<ref>{{cite web |url=https://docs.microsoft.com/en-gb/dotnet/visual-basic/programming-guide/program-structure/special-characters-in-code |title=Special Characters in Code (Visual Basic) |website=Microsoft Docs |publisher=Microsoft |date=15 September 2021 |archive-date=11 April 2022 |archive-url=https://web.archive.org/web/20220411195955/https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/program-structure/special-characters-in-code |url-status=live}}</ref>

In [[Forth (programming language)|Forth]], a colon ''precedes'' definition of a new word.<ref>{{cite web |url=https://forth-standard.org/standard/core/Colon |title=Core: Glossary |website=Forth Standard |publisher=Forth-Standard-Committee |archive-date=17 November 2015 |archive-url=https://web.archive.org/web/20151117054836/https://forth-standard.org/standard/core/Colon |url-status=live}}</ref>

[[Haskell]] uses a colon (pronounced as "[[cons]]", short for "construct") as an operator to add a [[data element]] to the front of a [[List (computing)|list]]:<ref>{{cite book |last1=O'Sullivan |first1=Bryan |last2=Stewart |first2=Don |last3=Goerzen |first3=John |date=2007–2008 |title=Getting Started |url=https://book.realworldhaskell.org/read/getting-started.html |publisher=Real World Haskell |access-date=8 November 2011 |url-status=live |archive-url=https://archive.today/20120710090552/http://book.realworldhaskell.org/read/getting-started.html |archive-date=10 July 2012}}</ref>

<syntaxhighlight lang="haskell">"child" : ["woman", "man"] -- equals ["child","woman","man"]</syntaxhighlight>

while a double colon <code>::</code> is read as "has type of" (compare [[Scope resolution operator#Haskell|scope resolution operator]]):<ref>{{cite book |first1=Miran |last1=Lipovača |date=April 2011 |url=https://learnyouahaskell.com/types-and-typeclasses |chapter=Types and Typeclasses |title=Learn You a Haskell for Great Good! |publisher=No Starch Press |isbn=978-1593272838 |access-date=8 November 2011 |archive-date=10 July 2012 |archive-url=https://archive.today/20120710015700/http://learnyouahaskell.com/types-and-typeclasses |url-status=live}}</ref>

<syntaxhighlight lang="haskell">("text", False) :: ([Char], Bool)</syntaxhighlight>

The [[ML (programming language)|ML]] languages (such as [[Standard ML]]) have the above reversed, where the double colon (<code>::</code>) is used to add an element to the front of a list; and the single colon (<code>:</code>) is used for type guards.<ref>{{cite book |last1=Milner |first1=Robin |author1-link=Robin Milner |last2=Tofte |first2=Mads |author2-link=Mads Tofte |last3=Harper |first3=Robert |author3-link=Robert Harper (computer scientist) |first4=David |last4=MacQueen |title=The Definition of Standard ML |edition=Revised |publisher=MIT Press |year=1997 |isbn=0-262-63181-4 |url=https://smlfamily.github.io/sml97-defn.pdf |archive-date=30 April 2020 |url-status=live |archive-url=https://web.archive.org/web/20200430075159/https://smlfamily.github.io/sml97-defn.pdf}}</ref>{{rp|pp=20, 70}}

[[MATLAB]] uses the colon as a binary operator to generate a vector, or to select a part of an extant matrix.

[[APL (programming language)|APL]] uses the colon:
* to introduce a [[Control flow|control structure]] element. In this usage it must be the first non-blank character of the line.<ref name="DyalogAPL">{{cite web |url=http://docs.dyalog.com/13.0/Dyalog%20APL%20Language%20Reference.v13.0.pdf |title=Dyalog APL Language Reference Manual |access-date=14 February 2012 |date=April 2011 |publisher=Dyalog Limited |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304040415/http://docs.dyalog.com/13.0/Dyalog%20APL%20Language%20Reference.v13.0.pdf |url-status=live}}</ref>{{Rp|p=64}}
* after a label name that will be the target of a <code>:goto</code> or a right-pointing arrow (this style of programming is deprecated and programs are supposed to use control structures instead).<ref name="DyalogAPL"/>{{Rp|p=64}}
* to separate a guard ([[Boolean expression]]) from its expression in a dynamic function.<ref name="DyalogAPL"/>{{Rp|p=111}} Two colons are used for an Error guard (one or more error numbers).<ref name="DyalogAPL"/>{{Rp|p=115}}
* Colon + space are used in class definitions to indicate inheritance.<ref name="DyalogAPL"/>{{Rp|p=135}}
* ⍠ (a colon in a box) is used by APL for its variant operator.<ref name="DyalogAPL"/>{{Rp|p=340}}

The colon is also used in many operating systems commands.<ref>{{cite web |url=https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#colon |title=colon – null utility |website=IEEE Std 1003.1-2017 |year=2018 |publisher=The Open Group |archive-date=17 October 2018 |archive-url=https://archive.today/20181017145503/http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html |url-status=live}}</ref>

In the [[esoteric programming language]] [[INTERCAL]], the colon is called ''two-spot'' and used to label a [[32-bit computing|32-bit]] variable, distinct from ''spot'' (.) to label a [[16-bit computing|16-bit]] variable.<ref>{{cite web |last1=Woods |first1=Donald R. |author1-link=Don Woods (programmer) |last2=Lyon |first2=James M. |year=1973 |url=http://oops.se/~urban/pit/intercal.ps |format=PS |url-status=dead |archive-url=https://web.archive.org/web/20110716084816/http://oops.se/~urban/pit/intercal.ps |title=INTERCAL reference manual |archive-date=2011-07-16 |access-date=2012-03-10}}</ref>{{Rp|p=3}}

===Addresses===
Internet URLs use the colon to separate the protocol (such as {{code|http:}}) from the [[hostname]] or [[IP address]].{{Ref RFC|3986|repeat=yes}}

In an [[IPv6 address#Representation|IPv6 address]], colons (and one optional double colon) separate up to 8 groups of 16 [[bit]]s in [[hexadecimal]] representation.{{Ref RFC|4291}} In a [[URL]], a colon follows the initial scheme name (such as Hypertext Transfer Protocol ([[HTTP]]) and [[File Transfer Protocol]] (FTP), and separates a [[port number]] from the [[hostname]] or [[IP address]].{{Ref RFC|3986}}

In [[Microsoft Windows]] [[filename]]s, the colon is reserved for use in [[fork (file system)#Microsoft|alternate data streams]] and cannot appear in a filename.<ref>{{cite web |url=https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/ffb795f3-027d-4a3c-997d-3085f2332f6f |title=[MS-FSCC]: 2.1.5 Pathname |website=Microsoft Docs |publisher=Microsoft |date=24 August 2020 |archive-date=22 October 2020 |archive-url=https://archive.today/20201022102028/https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/ffb795f3-027d-4a3c-997d-3085f2332f6f |url-status=live}}</ref> It was used as the directory separator in [[Classic Mac OS]], and was difficult to use in early versions of the newer [[BSD]]-based [[macOS]] due to code swapping the slash and colon to try to preserve this usage. In most systems it is often difficult to put a colon in a filename as the shell interprets it for other purposes.

[[CP/M]] and early versions of [[MSDOS]] required the colon after the names of devices, such as {{code|CON:}} though this gradually disappeared except for disks (where it had to be between the disk name and the required [[path (computing)|path representation]] of the file as in <code>C:\Windows\</code>). This then migrated to use in [[Uniform Resource Locator|URLs]].{{Ref RFC|3986|repeat=yes}}

===Text markup===
{{Unreferenced section|date=April 2022}}

It is often used as a single post-fix [[delimiter]], signifying a token keyword had immediately preceded it or the transition from one mode of character string interpretation to another related mode. Some applications, such as the widely used [[MediaWiki]], utilize the colon as both a pre-fix and post-fix delimiter.
<!-- Could work more wikimarkup into that as an example. --><!-- What is this trying to say? -->

In [[wiki markup]], the colon is often used to indent text. Common usage includes separating or marking comments in a discussion as replies, or to distinguish certain parts of a text.
{{markup
|<nowiki>
Normal text.
:Indented text by the means of a colon.
::The gap increases with colon number.
</nowiki>
|
Normal text.
:Indented text by the means of a colon.
::The gap increases with colon number.
}}

In human-readable text messages, a colon, or multiple colons, is sometimes used to denote an action (similar to how [[asterisk]]s are used){{Original research inline|date=May 2012}} or to emote (for example, in [[vBulletin]]). In the action denotation usage it has the inverse function of quotation marks, denoting actions where unmarked text is assumed to be dialogue. For example:

:'''Tom:''' Pluto is so small; it should not be considered a planet. It is tiny!
:'''Mark:''' Oh really? ::drops Pluto on Tom's head:: Still think it's small now?

Colons may also be used for sounds, e.g., ::click::, though sounds can also be denoted by asterisks or other punctuation marks.

Colons can also be used to represent eyes in [[emoticon]]s.