Concatenative programming language

A '''concatenative programming language''' is a point-free computer programming language in which all expressions denote functions, and the juxtaposition of expressions denotes function composition.<ref name="dobbscodetalk">{{cite magazine |last1=Diggins |first1=Christopher |date=2008-12-31 |url=http://drdobbs.com/blogs/architecture-and-design/228701299 |title=What is a concatenative language |magazine=Dr. Dobb's Journal |access-date=2013-07-01}}</ref> Concatenative programming replaces function application, which is common in other programming paradigms, with function composition as the default way to build subroutines.

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

...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, i.e., they typically do not represent the data structures they operate on with explicit names or identifiers. Instead they are function level – a function is defined as a pipeline, or a sequence of operations that take parameters from an implicit data structure on 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|archive-url=https://web.archive.org/web/20241008135442/https://concatenative.org/wiki/view/Concatenative%20language|archive-date=8 October 2024|url-status=dead|website=Concatenative.org|date=13 September 2013}}</ref>

The combination of compositional semantics with a 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 machines in the form of their instruction sets.<ref name="whymatters">{{cite web |last1=Purdy |first1=Jon |date=12 February 2012 |url=http://evincarofautumn.blogspot.com/2012/02/why-concatenative-programming-matters.html |title=Why Concatenative Programming Matters |website=The Big Mud Puddle |access-date=12 August 2025}}</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 |last1=von Thun |first1=Manfred |year=2011 |url=http://www.latrobe.edu.au/phimvt/joy/j08cnt.html |title=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. In concatenative programming practice, this is called 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 |last1=von Thun |first1=Manfred |year=2009 |url=http://www.latrobe.edu.au/philosophy/phimvt/joy/j02maf.html |title=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 is ever generated.<ref>{{cite report |last1=Baker |first1=Henry |year=1993 |url=http://home.pipeline.com/~hbaker1/ForthStack.html |title=Linear Logic and Permutation Stacks: The Forth Shall Be First |publisher=Nimble Computer Corporation |via=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, although Joy was the first language which was termed concatenative. Other concatenative languages are dc, Factor, Onyx, PostScript, RPL, Staapl,<ref name="Staapl">{{cite web |last1=Schouten |first1=Tom (zwizwa) |date= |url=http://zwizwa.be/staapl/ |title=Staapl: Forth on Scheme for Embedded Controllers |website=Zwizwa LLC |access-date=12 August 2025}}</ref> and experimental and discontinued ones including: Enchilada,<ref name="Enchilada">{{cite web |author1=rapido |author2=NewDave |author3=jacintheford |author4=goren |date=2 January 2024 |url=https://concatenative.org/wiki/view/Enchilada |title=Enchilada |website=Concatenative.org |access-date=12 August 2025}}</ref> Om,<ref name="Om">{{cite web |author1=sparist |date= |url=https://www.om-language.com/ |title=The Om Programming Language |website=Om-language.com |access-date=12 August 2025}}</ref> XY.<ref name="XY">{{cite web |last1=Apter |first1=Stevan |date=2004 |url=http://www.nsl.com/k/xy/xy.htm |title=The Concatenative Language XY |website=no stinking loops |access-date=12 August 2025}}</ref>

Most existing concatenative languages are stack-based. This is not required, and other models have been proposed.<ref name="XY"/><ref name="Enchilada"/><ref name="Om"/> Concatenative languages are currently used for embedded,<ref name="Staapl"/> desktop, and web programming, as 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 |last1=Purdy |first1=Jon |title=Kitten Programming Language |url=https://kittenlang.org/ |access-date=2025-03-31 |website=kittenlang.org}}{{Dead link|date=February 2026}}</ref>

==References== {{Reflist}}

==External links== * [http://www.concatenative.org/ Concatenative.org: Wiki], about concatenative programming

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