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Open Programming Language (OPL) is aprogramming language forembedded systems andmobile devices that run theoperating systemsEPOC andSymbian. It was released by the British companyPsion in 1984.

Originally designed for use on their classicPsion PDAs such as theSeries 3,5/5mx,Series 7, andnetBook–netPad, and the Psion producedMC218, OPL was provided as part of the standard application suite. It can also be installed on theNokia 9200,9300 and9500 Communicator seriesmobile telephone andpersonal digital assistant (PDA) and theSony EricssonP800,P900,P910 series. OPL is also included in Psion Teklogix industrial handhelds such as the Workabout mx, and it also appeared in the lesser known Oregon 'Osaris' organiser, a broadly compatible EPOC32 device that uniquely used version 4 of the OS. OPL is aninterpreted language similar toBASIC. A fullyVisual Basic-compatible language OVAL has also been developed.

The language was originally namedOrganiser Programming Language, developed byPsion Ltd for thePsion Organiser. Designed by Colly Myers with the first iteration implemented by Richard Harrison and Martin Stamp. The first implementation (without graphics) was for the original Psion Organiser (now referred to as the Psion Organiser I, 1984), and it came bundled with the Science, Finance and Mathdata packs. It became truly accessible as built-in software in thePsion Organiser II (1986), and the language went on to be used in thePsion Series 3 and later. After Psion retired from thepersonal digital assistant market, a project aiming to bring OPL to Symbian came to fruition, when the fledgling Symbian Developer Program released it asopen-source software. The language is now available onSourceForge in a project namedopl-dev.

The language is currently unavailable for Symbian OS v8 and later. With the subsequent retirement of the Symbian OS, it seems unlikely OPL will be made available for later generations of Symbian devices. As of 2010, Nokia device developers were encouraged to usePython for S60 instead (SeePython for S60).^{[citation needed]}

Here is the console version of a"Hello, World!" program:

PROC main:  PRINT "Hello World!"  PAUSE 40ENDP

(Source code taken from the PCDevPrimer in the OPL Wiki.)

And here is a GUI version for Nokia's Series 80 user interface:

CONST KKeyEnter%=13PROC hello:  dINIT "Hello"  dTEXT "","Hello World!"  dBUTTONS "OK",KKeyEnter%  DIALOGENDP

OPL is astructured programming language. OPL programs contain PROCedures, which are much like functions (subroutines) in other programming languages.

• The dINIT keyword in this example initializes a dialog box (intuitively enough, all dialog-box related functions begin with a letter 'd'; for clarity, this letter is in lower case, but the language is case independent). The first argument of the dialog is an optional string, which is used for the title of the dialog, displayed in the title bar.
• The dTEXT function displays text, with two compulsory arguments: a left-aligned 'prompt' string, and a main string.
• The dBUTTONS keyword allows you to put buttons on the dialog box - here there is a button with the text "OK". The second argument to each button is both the special notation of the shortcut key for that button and the dialog's return code, in this case the "Enter" key.
• Finally, the DIALOG keyword is required for the previously initialized dialog box to be shown on the screen.

An example:

PROCtest:dINIT"Your Challenge"dTEXT"","Will your answer to this question be no?"dBUTTONS"Yes",%y,"No",%nIFDIALOG=%yPRINT"No it wasn't!"ELSEPRINT"Yes it was!"ENDIFGETENDP

In this cruel interrogative program, the Yes button is assigned the shortcut of Ctrl+y, while No has Ctrl+n, represented by %y and %n respectively. The user's input from the DIALOG is tested in the IF statement, PRINTing appropriate responses to the screen. Note that the 'GET' keyword, which gets user input without using a dialog box, is here used simply to wait for a keypress before terminating the program (otherwise it would end immediately without giving time for the user to read the text). The output from DIALOG can also be stored in a variable.

Variables specific to a procedure must be declared with the LOCAL keyword; global variables are defined with the GLOBAL keyword.

The table below uses an example variable namedvar.

OPL interfaced with advanced Psion Series 3 features by means ofoperating system CALLs, but in the laterPsion Series 5mx this was changed to a so-calledOPXlibrary, stored in the systemread-only memory (ROM), termed the Z drive. 'OPX' libraries were also made available for theNokia 9210,Nokia 9300 andNokia 9500 Communicators, adding OPXs routines for handling Short Message Service (SMS) and managingBluetooth communication.

Other OPL features include those starting with a letter:g for graphical functions,m for menus, andd for dialogs.

• Psion Organiser
• Symbian

• Theopl-dev project
• OPL wiki onInternet Archive containing documents detailing OPL keywords, OPX interfaces and much other information
• OPL Blog by Symbian, now dead, butold versions are available from theInternet Archive
• Russian site about OPLArchived 6 December 2006 at theWayback Machine
• OPL programming tutorial

• Embedded systems
• Free mobile software
• Symbian OS
• Procedural programming languages
• BASIC programming language family
• Software using the GNU Lesser General Public License
• Computer-related introductions in 1984

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