View source for Joule (programming language)

{{Infobox programming language
|name = Joule
|logo =
|paradigm = [[multi-paradigm programming language|multi-paradigm]]: [[object-oriented programming|object-oriented]], [[distributed computing|distributed]], [[Dataflow]]
|year = 1996
|designer = E. Dean Tribble
|developer =
|latest release version =
|latest release date =
|typing = untyped
|implementations = 
|dialects =
|influenced_by = [[Logic Programming#Concurrent logic programming|Concurrent Logic Programming]], [[Actor model|Actors]]
|influenced = [[E (programming language)|E]]
}}
'''Joule''' is a capability-secure massively-[[concurrent programming language|concurrent]] [[dataflow programming]] language, designed for building [[distributed computing|distributed applications]].<ref>{{cite journal |last1=Miller |first1=Mark Samuel |authorlink=Mark S. Miller |title=Robust composition: towards a unified approach to access control and concurrency control |date=2006 |url=https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/873/index.html |publisher=Johns Hopkins University}}</ref> It is so concurrent that the order of statements within a block is irrelevant to the operation of the block. Statements are executed whenever possible, based on their inputs. Everything in Joule happens by sending messages. There is no [[control flow]]. Instead, the programmer describes the flow of data, making it a [[dataflow programming]] language.{{cn|date=March 2021}}

Joule development started in 1994 at ''Agorics'' in [[Palo Alto, California]].<ref>{{cite journal |last1=Fremont |first1=David |title=Waiting for the cyber-ax |journal=[[Spin (magazine)|Spin]] |date=October 1994 |volume=10 |issue=7 |page=88 |url=https://archive.org/details/sim_spin_1994-10_10_7/page/88/mode/2up?q=joule |language=English}}</ref> It is considered the precursor to the [[E programming language]].<ref>{{cite web |title=Related Links to Agoric Computing & Smart Contracts |url=http://erights.org/related.html |website=erights.org |quote=E's debt to Joule cannot be overstated.}}</ref><ref>{{cite web |title=The E Programmer's Manual |url=http://www.erights.org/history/original-e/programmers/index.html |publisher=Electric Communities |date=19 July 1996 |quote=The E programming language was largely inspired by the language Joule, currently being developed by Dean Tribble, Norm Hardy, and their colleagues at Agorics, Inc.}}</ref>

== Language syntax ==

[[Numerical digit|Numerals]] consist of [[ASCII]] digits 0–9; [[identifier]]s are [[Unicode]] sequences of digits, letters, and operator characters that begin with a letter. It is also possible to form identifiers by using Unicode sequences (including whitespace) enclosed by either straight (' ') or standard (‘ ’) single quotes, where the backslash is the escape character. [[Reserved word|Keyword]]s have to start with a letter, except the ''•'' keyword to send information. [[Operator (computer programming)|Operators]] consist of Unicode sequences of digits, letters, and operator characters, beginning with an operator character. [[Label (computer science)|Labels]] are identifiers followed by a colon (':').<ref name="Draft95">{{cite journal
 | date          = 20 December 2004
 | title         = Joule: Distributed Application Foundations: 4.2. Expressions
 | volume        = 1
 | pages         = 31–33
 | publisher     = Agorics, Inc.
 | accessdate    = 2012-08-29
 | url           = http://www.erights.org/history/joule/MANUAL.BK6.pdf
}}</ref>

At the root, Joule is an [[Imperative programming|imperative language]] and because of that a statement-based language. It has a rich expression syntax, which transforms easily to its relational syntax underneath. Complex expressions become separate statements, where the site of the original expression is replaced by a reference to the acceptor of the results channel. Therefore, nested expressions still compute completely concurrently with their embedding statement.<ref name="Draft95" />

    If amount <= balance
        • account withdraw: amount
    else
        • account report-bounce:
    end

An identifiers may name a channel to communicate with the server. If this is the case, it is said to be ''bound'' to that channel.<ref name="Draft95" />

== References ==
{{Reflist|2}}

==External links==
* [http://www.erights.org/history/joule/ Joule: Distributed Application Foundations]
* [http://c2.com/cgi/wiki?PromisePipelining C2: Promise Pipelining]

<!--Categories-->
[[Category:Concurrent programming languages]]
[[Category:Object-oriented programming languages]]
[[Category:Secure programming languages]]
[[Category:Capability systems]]


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