WHILE condition
WHILE expression

   Synopsis:
      Initiates a WHILE..LOOP loop

   Notes:
      Every WHILE statement must have a corresponding LOOP statement.
      The loop continues until the condition is evaluated as 'false'. The 
         contents of the loop won't be executed at all if the condition is
         evaluated as 'false' the first time it is checked.
      In contrast, a DO..UNTIL loop is guaranteed to be executed at least once.
      Following an EXIT WHILE statement, the loop terminates immediately.
         Execution resumes after the LOOP statement.

   Availability:
      WHILE is not available in scripts with primitive line numbers.

   Examples:
      ! Print the numbers 1 to 10 in sequence
      LET count = 0
      WHILE count < 11
         LET count = count + 1
         PRINT count
      LOOP

      ! This loop runs forever
      WHILE 1
         PRINT "Hello, world!"
      LOOP

      ! This loop doesn't run once
      WHILE 0
         PRINT "Hello, world!"
      LOOP     
