IF ... THEN operator

The IF ... THEN operator creates an action that implements branching with one condition (single form).

Syntax

IF condition 
THEN action
[ELSE alternativeAction]

Description

The IF ... THEN operator creates an action that implements branching with one condition. When this action is executed, the condition is checked: if it is met, the action specified after the keyword THEN is called. If it is not met, the action specified after the keyword ELSE is called (if this block is specified).

An ELSE branch attaches to the nearest preceding operator that admits one and does not have one yet. If the action after THEN is written without braces and is itself an operator whose syntax ends with an optional ELSE branch — ASK, INPUT, DIALOG and IMPORT when written with DO, FOR, REQUEST, CASE or another IF ... THEN — the ELSE that follows it becomes the branch of that operator, not of this one. No error or warning is reported, and when the condition is not met nothing is executed. To attach ELSE to the IF ... THEN operator, enclose the action after THEN in braces.

Parameters

• condition

  Expression defining a condition. If the value of the expression does not equal NULL, then the condition is met and the action specified after the keyword THEN is called.

• action

  Context-dependent operator that describes the action that will be executed when the corresponding condition is met.

• alternativeAction

  Context-dependent operator that describes an action that will be executed if the condition is not met.

Examples

// Action that compares the value of the count property to 3 and displays a message to the user
moreThan3(obj)  {
    IF count(obj) > 3 THEN
        MESSAGE '>3';
    ELSE
        MESSAGE '<=3';
}

checkNullName (Store st) {
    IF NOT name(st) THEN
        MESSAGE 'Name is null';
}

// ELSE belongs to ASK (the cancellation branch), not to IF: when confirm() is NULL, nothing is executed
sendOrAsk (Order o)  {
    IF confirm() THEN
        ASK 'Send the order?' DO send(o);
    ELSE
        send(o);
}

// the braces attach ELSE to IF
sendOrAskFixed (Order o)  {
    IF confirm() THEN {
        ASK 'Send the order?' DO send(o);
    } ELSE
        send(o);
}