The while statement repeats its code while a specified condition is true. while is not standard in Scheme or Common Lisp, but is found in many languages. Its format is:

      (while condition code )

The condition is tested first; if it is true (anything other than #f), then the code is executed, and the operation is repeated. The value of while is #[undefined].

while can be used to attempt to solve a problem, stopping when a solution is reached. Of course, this has the danger of an infinite loop if no solution is found.

; sqrt using while
(define (mysqrt x)
  (let ((estimate 1.0))
    (while (> (abs (- (square estimate) x))
              1.0e-8)
      (set! estimate
            (/ (+ estimate
                  (/ x estimate))
               2)) )
    estimate))

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