layout/while

Symbol: layout/while

Use-case: Block syntax for a while loop with an optional else peer. The read result keeps the while head and is compiled by compile/while.

Behaviour: The header is while TEST, one test expression. Body forms are appended to the header list with no begin wrapper, giving (while TEST BODY...). else is the only peer gathered; its body is appended as a final (else: BODY...) clause rather than merged into the loop body. Rules: else takes no arguments, and at most one else peer may appear.

Syntax:

while TEST:
  BODY
else:
  BODY

Examples:

while (< x 3):
  (print x)
;; -> (while (< x 3) (print x))

while (< x 3):
  (print x)
  set! x (+ x 1)
else:
  (print "done")
;; -> (while (< x 3) (print x) (set! x (+ x 1)) (else: (print "done")))

var total 0
var x 0

while (< x 3):
  set! total (+ total x)
  set! x (+ x 1)
else:
  (print "while done" total)
;; prints: while done 3

Also: special form while.