Editing Forth (programming language) (section)

{{Short description|Stack-based programming language}}
{{Redirect|FORTH||Forth (disambiguation)}}
{{Infobox programming language
| name = Forth
| paradigm = [[Concatenative programming language|concatenative]] ([[Stack-oriented programming|stack-based]]), [[Procedural programming|procedural]], [[Reflective programming|reflective]]
| year = {{start date and age|1970}}
| designer = [[Charles H. Moore]]
| typing = Typeless
| implementations = SwiftForth (Forth, Inc.)<br/>[[Gforth]] (GNU Project)<br/>VFX Forth (MicroProcessor Engineering)
| influenced = [[Bitcoin#Transactions|Bitcoin Script]], [[Factor (programming language)|Factor]], [[Joy (programming language)|Joy]], [[RPL (programming language)|RPL]], [[Rebol]], [[STOIC]]
| file_ext = .fs, .fth, .4th, .f, .forth{{cn|date=April 2022}}
| website = {{URL|https://forth-standard.org}}
}}

'''Forth''' is a [[Stack-oriented programming|stack-oriented]] [[programming language]] and interactive [[integrated development environment]] designed by [[Charles H. Moore|Charles H. "Chuck" Moore]] and first used by other programmers in 1970. Although not an [[acronym]], the language's name in its early years was often spelled in [[all caps|all capital letters]] as ''FORTH''. The FORTH-79 and FORTH-83 implementations, which were not written by Moore, became ''[[de facto]]'' standards, and an official [[technical standard]] of the language was published in 1994 as ANS Forth. A wide range of Forth derivatives existed before and after ANS Forth. The [[free and open-source software]] [[Gforth]] implementation is actively maintained, as are several [[Commercial software|commercially]] supported systems.

Forth typically combines a compiler with an integrated command shell,{{efn|There are exceptions, such as Ulrich Hoffmann's preForth [http://www.euroforth.org/ef18/papers/hoffmann-slides.pdf][http://www.euroforth.org/ef18/papers/hoffmann.pdf] and Tom Zimmer's TCOM}} where the user interacts via [[subroutine]]s called ''words''. Words can be defined, tested, redefined, and debugged without recompiling or restarting the whole program. All syntactic elements, including variables, operators, and control flow, are defined as words. A [[stack (abstract data type)|stack]] is used to pass parameters between words, leading to a [[Reverse Polish notation]] style.

For much of Forth's existence, the standard technique was to compile to [[threaded code]], which can be interpreted faster than [[bytecode]]. One of the early benefits of Forth was size: an entire development environment—including compiler, editor, and user programs—could fit in memory on an 8-bit or similarly limited system. No longer constrained by space, there are modern implementations that generate [[Optimizing compiler|optimized]] [[machine code]] like other language compilers. The relative simplicity of creating a basic Forth system has led to many personal and proprietary variants, such as the custom Forth used to implement the bestselling 1986 video game ''[[Starflight]]'' from [[Electronic Arts]].<ref name="maher">{{cite web|last1=Maher|first1=Jimmy|title=Starflight|url=https://www.filfre.net/2014/10/starflight/|website=The Digital Antiquarian|date=October 28, 2014|access-date=April 29, 2023}}</ref>

Forth is used in the [[Open Firmware]] [[boot loader]], in [[spaceflight]] applications<ref name="oSWRm">[https://web.archive.org/web/20101024223709/http://forth.gsfc.nasa.gov/ NASA applications of Forth] (original NASA server no longer running, copy from archive.org)</ref> such as the [[Philae (spacecraft)|''Philae'' spacecraft]],<ref name="zYmBe">{{cite web|title=Intersil's RTX processors and Forth software controlled the successful Philae landing|url=https://mpeforth.com/press/MPE_PR_From_Telescope_to_Comet_2014_11_13.pdf |access-date=April 29, 2023|website=MicroProcessor Engineering Limited|date=October 13, 2014}}</ref><ref name="sgEMh">{{cite web|title=Here comes Philae! Powered by an RTX2010|url=https://www.cpushack.com/2014/11/12/here-comes-philae-powered-by-an-rtx2010/|website=The CPU Shack Museum|date=October 12, 2014|access-date=April 29, 2023}}</ref> and in other embedded systems which involve interaction with hardware. 

Moore developed a series of microprocessors for executing compiled Forth-like code directly and experimented with smaller languages based on Forth concepts, including cmForth and [[colorForth]]. Most of these languages were designed to support Moore's own projects, such as chip design.