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Line 1: In computer programming, a '''promise''' (also known as a '''future''' in some languages) is a placeholder for a result that is not yet known, usually because a computation has not yet finished or a message from a remote party has not yet arrived. The use of promises can dramatically reduce latency in distributed systems because it enables pipelining of messages, called '''promise pipelining''' [http://www.erights.org/elib/distrib/pipeline.html] [http://c2.com/cgi/wiki?PromisePipelining]. == Known implementations == This [[concurrent programming]] technique of ~~promises/futures~~ was invented by the MIT Actors group in the 1970s. It became more well known by its inclusion in [[MultiLisp programming language\|MultiLisp]]. The use of logic variables for communication in concurrent logic programming languages is quite similar. These started with "Prolog with Freeze" and "IC Prolog", and became a true concurrency primitive with Concurrent Prolog, Flat Concurrent Prolog, Parlog, Vulcan, Janus, Mozart/Oz, Flow Java, and Alice. The single assignment "I-var" from data flow languages, included in Reppy's "Concurrent ML", is much like the concurrent logic variable. This pipelining technique (of using promises/futures to overcome latency) was invented independently twice in the 1980s. It was invented at [[Project Xanadu]] (circa 1989) and by [[Barbara Liskov]] in 1988. Languages containing "promises/futures/concurrent logic variables/I-vars" include [[Alice programming language\|Alice]] and [[MultiLisp programming language\|MultiLisp]].▼ ▲Languages containing "promises/futures/concurrent logic variables/I-vars" include ~~[[Alice programming language\|Alice]] and [[MultiLisp programming language\|MultiLisp]].~~: ~~Languages containing promise pipelining include [[Joule programming language\|Joule]] and [[E programming language\|E]].~~ * [[Alice programming language\|Alice]] * [[Oz programming language\|Oz]] * [[MultiLisp programming language\|MultiLisp]] Languages containing promise pipelining include: * [[Joule programming language\|Joule]] * [[E programming language\|E]] ==External references== * [http://c2.com/cgi/wiki?PromisePipelining PromisePipelining] on the [http://c2.com/cgi/wiki?FrontPage C2 wiki] [[Category:Software design patterns]]

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