while

The while keyword executes a statement block.

Purpose

This statement is used in the action part of rules or in functions to execute a statement block numerous times.

Context

Functions or rule actions

Syntax

while (test) [{statement1; ... statementn;}]

Description

The test argument can be any legal test, as in the Java™ programming language. The statement block can execute any IRL statement, arithmetic expressions, and method calls. Empty statement blocks are valid. If you specify only one statement block, the braces {} are not mandatory.

Example

rule StockDropWarning {
   when {
      ?c:Client(?a:account_number;?p:percentWarningMark);
      ClientStockList(account_number == ?a; ?s:stockList);
   }
   then {
      Enumeration ?enum = ?s.elements();
      while (?enum.hasMoreElements()) {
         Stock ?x = (Stock)enum.nextElement();
         if (((1.-?p)*?x.purchasePrice) > ?x.currentPrice) {
            System.out.println("Dear "+ ?c.name +  "Your stock "
            + ?x.ticker + " has dropped " + ( (?x.purchasePrice
            - ?x.currentPrice) / ?x.purchasePrice ) + 
            " percent.");
         }
      }
   }
};

The rule StockDropWarning checks the percent change of a client’s stocks and warns if a stock price is below its purchase price by a certain percentage. The condition Client returns an account number in variable ?a and a decimal value percentWarningMark in variable ?p. The second condition, ClientStockList, returns a stock list in variable ?s corresponding to the account number equal to ?a. In the action part of the rule, the while statement iterates on every stock in the stock list ?s and check the difference between the purchase price and the current price. If the stock price decreased in ?p percent below the purchase price, the println function in the action statement prints a message.