Opa (programming language): Difference between revisions

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{{short description|Programming language for developing scalable web applications}}

{{Infobox programming language

| name = Opa

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'''Opa''' is a [[programming language]] for developing [[Scalability|scalable]] [[web application]]s. It is [[free and open-source software]] released under a [[GNU Affero General Public License]] (AGPLv3), and an [[MIT License]].

It can be used for both [[client-side scripting|client-side]] and [[server-side scripting]], where complete programs are written in Opa and subsequently compiled to [[Node.js]] on a [[Server (computing)|server]] and [[JavaScript]] on a [[Client (computing)|client]], with the [[compiler]] automating all communication between the two.<ref>{{cite web |last1=Koprowski |first1=Adam |url=http://www.developer.com/open/opa-vs.-node.js-javascript-framework-comparison.html |title=Node.js vs. Opa: Web Framework Showdown |publisher=developer.com |date=24 February 2012 |access-date=1 March 2012 |archive-date=4 November 2012 |archive-url=https://web.archive.org/web/20121104144936/http://www.developer.com/open/opa-vs.-node.js-javascript-framework-comparison.html |url-status=dead }}</ref><ref>Opa supports various server-side backends, Nodejs being the most popular one.</ref> Opa implements [[Strong and weak typing|strong]], [[static typing]], which can be helpful in protecting against security issues such as [[SQL injection]]s and [[cross-site scripting]] attacks.<ref>{{cite journal |last1=Robertson |first1=William |last2=Giovanni |first2=Vigna |year=2009 |url=http://www.mendeley.com/research/static-enforcement-of-web-application-integrity-through-strong-typing/ |title=Static Enforcement of Web Application Integrity Through Strong Typing |journal=SSYM'09 Proceedings of the 18th Conference on USENIX Security Symposium}}{{Dead link|date=April 2020 |bot=InternetArchiveBot |fix-attempted=yes}}</ref>

The language was first officially presented at the Open Worldwide Application Security Project ([[OWASP]]) conference in 2010,<ref>{{cite web |date=June 2010 |publisher=OWASP

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The core language is [[Functional programming|functional]] and has a static [[type system]] with [[type inference]]. Opa also provides sessions which encapsulate an [[Imperative programming|imperative]] state and communicate using [[message passing]], similar to [[Erlang (programming language)|Erlang]] processes. Opa provides many structures or functions that are common in [[web development]], as [[first-class citizen]] objects, for instance [[HTML]]<ref>{{cite web|url=http://www.i-programmer.info/news/98-languages/2961-opa-a-unified-approach-to-web-programming.html |title=Opa – a unified approach to web programming |publisher=i-Programmer |date=28 August 2011}}</ref> and [[parser]]s, based on [[parsing expression grammar]]s.<ref>{{cite journal |last1=Koprowski |first1=Binsztok |year=2011 |url=http://www.lmcs-online.org/ojs/viewarticle.php?id=708&layout=abstract |title=TRX: A Formally Verified Parser Interpreter |journal=Logical Methods in Computer Science}}</ref> Because of this adhesion between the language and web-related concepts, Opa is not intended for non-web applications (for instance [[desktop application]]s).<ref>{{cite web |url=http://linuxfr.org/news/opa-un-nouveau-langage-pour-le-d%C3%A9veloppement-d%E2%80%99applications-web |title=Opa, un nouveau langage pour le développement d'applications Web|publisher=LinuxFr |language=Fr |date=22 June 2011}}</ref>

The 0.9.0 release in February 2012 introduced database mapping technology for the non-relational, document-oriented database [[MongoDB]], similar to [[object-relational mapping]].<ref>{{cite webnews|url=http://docnews.opalangidg.orgno/#!cw/manual/Helloart.cfm?id=36C6A408-F2EE-database3929-CB53260EBA6B884F|title=HelloProgramming Opa: Web development, databasereimagined|publisher=Opa Documentation[[Computerworld]]|access-date=1 February 2012-02-22|archive-url=https://web.archive.org/web/20140112111933/http://doc.opalang.org/#!/manual/Hello--database|archive-date=2014-01-12|url-status=dead}}</ref><ref>{{cite2 web|url=http://doc.opalang.org/#!/manual/Low-level-MongoDB-support|title=Low-levelOctober MongoDB support|publisher=Opa Documentation2016|access-date=22 February 2012-02-22|archive-url=https://web.archive.org/web/2014011211193320161002184533/http://doc.opalang.org/#!/manual/Low-level-MongoDB-support|archive-date=2014-01-12|url-status=dead}}</ref><ref>{{cite news|url=http://news.idg.no/cw/art.cfm?id=36C6A408-F2EE-3929-CB53260EBA6B884F|titleurl-status=Programming Opa: Web development, reimagined|publisher=[[Computerworld]]|date=1 February 2012dead}}</ref>

The 1.1.0 release in February 2013 also added support for [[PostgreSQL]], paving the way for the support of several [[SQL]] databases.

== Examples ==

=== Hello world ===

The traditional [["Hello, World!" program]], producing a web server that serves a static page with "Hello, web!" as its content, can be written in Opa as:<ref>{{cite web |url=http://www.morganhill.co.uk/cloud/opa-the-cloud-language-test-drive/ |title=Opa, the cloud language – a test drive |date=26 July 2011 |publisher=Morgan Hill |last1=Aitken |first1=Alastair |access-date=6 September 2011 |archive-url=https://web.archive.org/web/20110925044819/http://www.morganhill.co.uk/cloud/opa-the-cloud-language-test-drive/ |archive-date=25 September 2011 |url-status=dead}}</ref>

<syntaxhighlight lang="opa">

Server.start(Server.http,

{ title: "Hello"

, page: function() { <h1>Hello, web!</h1> }

}

)

</syntaxhighlight>

It can be compiled to a stand-alone executable JavaScript file with:

<syntaxhighlight lang="bash">

$ opa hello_web.opa

</syntaxhighlight>

Running the resulting executable JavaScript file launches the web application:

<syntaxhighlight lang="bash">

$ ./hello_web.js

</syntaxhighlight>

== See also ==

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[[Category:Cross-platform free software]]

[[Category:Programming languages created in 2011]]

[[Category:Software using the GNU AGPLAffero licenseGeneral Public License]]

[[Category:Software using the MIT license]]

[[Category:2011 software]]