Open (programming language)

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The Open Programming Language (OPL) is an embedded programming language for portable devices that run the Symbian Operating System, which can be found on e.g. the Nokia 9200, 9300 and 9500 Communicator series mobile telephone/PDA and the Sony Ericsson's P800, P900, P910 series. On classic Psion PDAs such as the Series 3/5/5mx/7 and netBook/netPad, OPL is part of the standard application suite. OPL is an interpreted language similar to BASIC.

The language was originally called Organiser Programming Language developed by Psion Ltd for the Psion Organiser. The first implementation (without graphics) was for the Psion Organiser II (1986) and the language went on to be used in the Psion Series 3 and later. After Psion retired from the PDA market, the project was changed to open source and the acronym was re-interpreted. The language is now developed on SourceForge in the opl-dev project.

To the grievance of the large OPL developer community, the language is not available from Symbian OS v8 and later, mainly due to lack of interest and support from major Symbian licencees Nokia and Sony Ericsson. Hence, OPL will most likely never be made available for the newer generation of Symbian OS phones such as Sony Ericsson P990, M600, W950 and Nokia E61 and E90.

1 Examples
- 1.1 Testing Dialog Responses
- 1.2 Variable Types
2 Minutiae
3 See also
4 External links

[edit] 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:

CONST KKeyEnter%=13

PROC hello:
  dINIT "Window Title"
  dTEXT "","Hello World"
  dBUTTONS "OK",KKeyEnter%
  DIALOG
ENDP

OPL is a structured programming language. 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 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.

[edit] 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 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.

[edit] Variable Types

The table below uses an example variable called 'var'.

Data Type	Syntax
Floating Point	var
Integer	var%
Long Integer	var&
String	var$(length)

[edit] Minutiae

OPL interfaced with advanced Psion Series 3 features by means of operating system CALLs, but in the later Psion Series 5mx this was changed to a so-called 'OPX' library, stored in the system ROM (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.