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Open programming language

The Open Programming Language (OPL) is a programming language for the Symbian OS that can be found on e.g. the Nokia 9200 Communicator series mobile telephone/personal digital assistant. OPL is an interpreted language similar to BASIC programming language.

The language was originally called Organiser Programming Language developed by Psion for the legendary Psion Organiser, and used on their Psion 3 and later PDAs. After the project was changed to open source, the acronym was re-interpreted. The language is now developed on SourceForge in the opl-dev project.

=Examples=

Here is a small Hello world program:

PROC main: PRINT Hello World PAUSE 40 ENDP

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

And here is a GUI version:

PROC hello: dINIT Window Title dTEXT , Hello World dBUTTONS OK ,13 DIALOG ENDP

OPL programs contain PROCedures, which are much like functions 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 you can mix the case up in your own programs). 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 (in case that was not obvious), 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 we have a button with the text OK . The second argument to each button text is both the special notation of the shortcut key for that button and the dialog s return code.

Finally, don t forget the DIALOG keyword, which is required for the previously initialized dialog box to be shown on the screen.

==Testing Dialog Responses==

An example:

PROC test: dINIT Your Challenge dTEXT , Will your answer to this question be no dBUTTONS Yes ,%y, No ,%n IF DIALOG=%y PRINT No it wasn t! ELSE PRINT Yes it was! ENDIF GET ENDP

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 groan at the ridiculousness of the question asked them). 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.

==Variable Types==

The table below uses an example variable called var .

Data TypeSyntax Floating Pointvar Integervar% Long Integervar& Stringvar$( length )

=Minutiae=

OPL interfaced with advanced Psion Series 3 features by means of operating system CALLs, but in the later Psion 5 this was changed to a so-called OPX library, stored in the system Read-only memory (the Z drive).

Other OPL features include those with a letter g at the beginning, for graphical functions; and those with a letter m , for menus. If only all programming languages were this simple.

=See also=

Organiser Programming Language

=External links=

[http://opl-dev.sourceforge.net/ Homepage of the opl-dev project]

[http://www.symbiandiaries.com/opl/ OPL Blog by Symbian]

[http://www.allaboutopl.com/wiki/OPLWikiHome Official OPL documentation as Wiki]