Editing Concatenative programming language

{{short description|Type of programming language}}
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A '''concatenative programming language''' is a [[Point-free programming|point-free]] computer [[programming language]] in which all expressions denote [[Function (mathematics)|functions]], and the [[juxtaposition]] of [[Expression (computer science)|expressions]] denotes [[function composition]].<ref name="dobbscodetalk">{{cite web|url=http://drdobbs.com/blogs/architecture-and-design/228701299 |title=Christopher Diggins: What is a concatenative language |publisher=Drdobbs.com |date=2008-12-31 |access-date=2013-07-01}}</ref> Concatenative programming replaces [[function application]], which is common in other programming styles, with [[function composition (computer science)|function composition]] as the default way to build [[subroutine]]s.

==Example==
For example, a nesting of operations in an applicative language like the following:

<syntaxhighlight lang="javascript">
baz(bar(foo(x)))
</syntaxhighlight>

...is written in a concatenative language as a sequence of functions:<ref>{{cite web | url=http://concatenative.org/wiki/view/Concatenative%20language/Name%20code%20not%20values | title=Name code not values | publisher=Concatenative.org | access-date=13 September 2013}}</ref>

 x foo bar baz

Functions and procedures written in concatenative style are not [[Value-level programming|value level]], i.e. they typically do not represent the data structures they operate on with explicit names or [[identifier#In computer science|identifiers]]. Instead they are [[Function-level programming|function level]]{{Spaced en dash}}a function is defined as a [[pipeline (software)|pipeline]], or a sequence of operations that take parameters from an implicit [[data structure]] upon which all functions operate, and return the function results to that shared structure so that it will be used by the next operator.<ref>{{cite web | url=http://concatenative.org/wiki/view/Concatenative%20language | title=Concatenative language | publisher=Concatenative.org | access-date=13 September 2013}}</ref>

The combination of compositional [[Semantics of programming languages|semantics]] with a [[Syntax of programming languages|syntax]] that mirrors such a semantic makes concatenative languages highly amenable to algebraic manipulation of programs;<ref>{{cite web|url=http://www.latrobe.edu.au/philosophy/phimvt/joy/j00rat.html|archive-url=https://web.archive.org/web/20110115151536/http://www.latrobe.edu.au/philosophy/phimvt/joy/j00rat.html|archive-date=2011-01-15|title=Rationale for Joy, a functional language}}</ref> although it may be difficult to write mathematical expressions directly in them.<ref name="whymatters"/> Concatenative languages can be implemented efficiently with a [[stack machine]], and are commonly present implicitly in [[virtual machine]]s in the form of their [[instruction set]]s.<ref name="whymatters">{{cite web | url=http://evincarofautumn.blogspot.com.es/2012/02/why-concatenative-programming-matters.html | title=Why Concatenative Programming Matters | access-date=13 September 2013}}</ref>

==Properties==
The properties of concatenative languages are the result of their compositional syntax and semantics:

* The reduction of any expression is the simplification of one function to another function; it is never necessary to deal with the application of functions to objects.<ref>{{cite web|url=http://www.latrobe.edu.au/phimvt/joy/j08cnt.html |title=von Thun, Manfred: Joy compared with other functional languages |archive-url=https://web.archive.org/web/20111006225512/http://www.latrobe.edu.au/phimvt/joy/j08cnt.html |archive-date=2011-10-06}}</ref>
* Any subexpression can be replaced with a name that represents the same subexpression. This is referred to in the concatenative community as [[Code refactoring|factoring]] and is used extensively to simplify programs into smaller parts.
* The syntax and semantics of concatenative languages form the algebraic structure of a [[monoid]].<ref>{{cite web|url=http://www.latrobe.edu.au/philosophy/phimvt/joy/j02maf.html |title=von Thun, Manfred: Mathematical foundations of Joy |archive-url=https://web.archive.org/web/20100731060810/http://www.latrobe.edu.au/philosophy/phimvt/joy/j02maf.html |archive-date=2010-07-31}}</ref>
* Concatenative languages can be made well-suited to an implementation inspired by [[linear logic]] where no [[Garbage (computer science)|garbage]] is ever generated.<ref>{{cite web |url=http://home.pipeline.com/~hbaker1/ForthStack.html |title=Henry Baker: Linear Logic and Permutation Stacks — The Forth Shall Be First |publisher=Home.pipeline.com |access-date=2013-07-01 |archive-url=https://web.archive.org/web/20140724091729/http://home.pipeline.com/~hbaker1/ForthStack.html |archive-date=2014-07-24 |url-status=dead }}</ref>

==Implementations==
The first concatenative programming language was [[Forth (programming language)|Forth]], although [[Joy (programming language)|Joy]] was the first language to call itself concatenative. Other concatenative languages are [[Dc_(computer_program)|dc]], [[Factor (programming language)|Factor]], Onyx, [[PostScript]], and [[RPL (programming language)|RPL]].

Most existing concatenative languages are [[stack-based]]; this is not a requirement and other models have been proposed.<ref>{{cite web|url=http://www.nsl.com/k/xy/xy.htm |title=The Concatenative Language XY |publisher=Nsl.com |access-date=2013-07-01}}</ref><ref>{{cite web|url=http://www.enchiladacode.nl/ |title=The Enchilada Programming Language |publisher=Enchiladacode.nl |access-date=2013-07-01}}</ref><ref>{{cite web|url=http://www.om-language.org/ |title=The Om Programming Language |publisher=Om-language.org |access-date=2013-07-01}}</ref> Concatenative languages are currently used for [[embedded systems|embedded]], [[Application software|desktop]], and [[web programming]], as [[Target language (computing)|target languages]], and for research purposes.

Most concatenative languages are [[dynamically typed]]. Exceptions include the [[statically typed]] Cat language<ref>{{cite web|url=http://www.cat-language.com/manual.html |title=Cat Specification |publisher=Cat-language.com |access-date=2013-07-01 |archive-url=https://web.archive.org/web/20150205081218/http://cat-language.com/manual.html |archive-date=2015-02-05}}</ref> and its successor, Kitten<ref>{{Cite web |title=Kitten Programming Language |url=https://kittenlang.org/ |access-date=2025-03-31 |website=kittenlang.org}}</ref>.

==See also==
* [[Function-level programming]]
* [[Homoiconicity]]
* [[Stack-oriented programming language]]
* [[Tacit programming]]

==References==
{{Reflist}}

==External links==
* [http://www.concatenative.org concatenative.org: A wiki about concatenative languages]
* [http://zwizwa.be/staapl Staapl: Forth on Scheme for Embedded Controllers]
* [http://www.enchiladacode.nl The Enchilada Programming Language]
* [http://www.nsl.com/k/xy/xy.htm The Concatenative Language XY]
* [http://om-language.org The Om Programming Language]

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