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. 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. Variable types The table below uses an example variable named var. 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 read-only memory (ROM), termed the Z drive. 'OPX' libraries were also made available for the Nokia 9210, Nokia 9300 and Nokia 9500 Communicators, adding OPXs routines for handling Short Message Service (SMS) and managing Bluetooth communication. Other OPL features include those starting with a letter: g for graphical