Volume 6A: Motif Programming Manual

Motif widget class such as XmPushButton or XmForm in a callback declaration. Finally, you can indicate that an

argument is expected, but not restrict its type, by specifying the special type−name any. If you use the any specifier,

you should take extra care to ensure that references to the procedure elsewhere in the UIL module do not pass values

to the callback that might crash your application. This problem has been fixed as of Motif Release 1.2.3.

The UIL compiler makes sure that the use of a callback is consistent with its declaration. If you declare a callback as

taking no arguments, you cannot pass an argument to the callback when you use it. Likewise, when a callback does

take an argument, you must provide one when you use the routine, and the argument must match the type in the

declaration. You can pass an argument whose type does not match the declaration if the UIL automatic type

conversions described earlier provide for it. For example, you can pass a string to a callback that is declared as

taking a compound_string. If the use of a callback does not agree with its declaration, the UIL compiler generates

an error, and the module is not compiled successfully. The following code fragment shows how you might use the

print and quit callbacks:

object close : XmPushButton {

callbacks {

XmNarmCallback = procedure print ("Armed!");

XmNactivateCallback = procedure quit();

};

};

When a callback specified in a UIL module is invoked at run−time, the argument, if any, is passed to the callback ...