Learning WML, and WMLScript

Variables

WMLScript provides only local variables and access to the WML variables (which are always string-valued) from the browser context. There are no global variables, and there is no way to have any values persist from call to call. When a function returns, all its variables are lost.

A WMLScript variable can take a value of any of the five datatypes, including invalid. Variables are declared with the var statement. Any number of variables may be specified, separated by commas such as:

var foo;
var x, y, z;
var a, b, c, d, e, f, g, h, i, j;

Variables must be declared before use, so for example the following is incorrect:

function foo ( )
{
    wibble = 2;
    var wibble;
}

All variables are implicitly initialized to the empty string, "". If some other initial value is required, an optional initializer may be included with the declaration:

var foo = 17, bar = 42;

This is completely equivalent to:

var foo, bar;
foo = 17;
bar = 42;

This means that the usual pattern of a WMLScript function is to first read variables out of the WML browser context, then process those values in some way, then write back new values to the context, and run a task (usually either a <refresh> or a <go>). For an illustration, see Example 10.1. The updated display reflects the new values of variables. I will return to browser variables in later chapters.

Example 10-1. Outline of a Function Called from WML

extern function called_from_wml ( ) { /* First read variables from browser context. * These could also be passed in ...