10.1.5 WHILE Modifier
  The WHILE modifier repeats a statement as long as a
  conditional expression is true. Like the UNTIL and FOR
  modifiers, the WHILE modifier lets you create single-line
  loops. In the following example, BASIC replaces the value of
  A with A /2, as long as the absolute value of A is greater than
  one-tenth. Note that you can inadvertently create an infinite
  loop if the terminating condition is never reached.
  A = A / 2 WHILE ABS(A) > 0.1