Learning WML, and WMLScript

Conditions

Conditional statements in WMLScript behave just like they do in C. The simplest form looks like:

if (condition) statement-when-true

The condition is simply any expression. It’s evaluated, and if the result can be converted to Boolean true, the statement-when-true is executed. For example:

if (x > max)
    max = x;

An else clause can also be added, looking like:

if (condition) statement-when-true
else
    statement-when-false

If the condition can be converted to Boolean true, statement-when-true is executed, but if the condition converts to Boolean false or can’t be converted, statement-when-false is executed. For example:

if (number == 1)
    result = "1 apple";
else
    result = number + " apples";

Sometimes, the statement-when-false is itself another if. There is nothing special about this: the first condition is evaluated, and if it’s false or can’t be converted, the second if is executed. For example:

if (x > max)
    max = x;
else if (x < min)
    min = x;

Matters are more interesting if the statement-when-true contains an if with an else clause. For example, consider:

if (x)
    if (y)
        foo ( );
    else
        bar ( );

What exactly does this mean? The indentation suggests that the else belongs with the second if, but the compiler doesn’t look at the indentation: all spaces are the same to it. The same code could equally be interpreted as:

if (x)
    if (y)
        foo ( );
else
    bar ( );

(That is, with the else attached to the first if.)

This ambiguity is known as the dangling else problem and affects many different programming ...