5.14 while

A normal while loop starts with the while keyword, followed by an opening parenthesis (, the condition expression and a closing parenthesis ). After that follows the loop body expression:

while(condition) expression;

The condition expression has to be of type Bool.

Upon each iteration, the condition expression is evaluated. If it evaluates to false, the loop stops, otherwise it evaluates the loop body expression.

class Main {
  static public function main() {
    var f = 0.0;
    while (f < 0.5) {
      trace(f);
      f = Math.random();
    }
  }
}

This kind of while-loop is not guaranteed to evaluate the loop body expression at all: If the condition does not hold from the start, it is never evaluated. This is different for do-while loops.