37 lines
831 B
Racket

#lang racket/base
(require (for-syntax racket/base br/syntax)
br/define)
(provide (all-defined-out))
(define-macro (until COND EXPR ...)
#'(let loop ()
(unless COND
EXPR ...
(loop))))
(define-macro (while COND EXPR ...)
#'(let loop ()
(when COND
EXPR ...
(loop))))
(define-macro (forever . EXPRS)
;; todo: would be better with a syntax parameter
(with-pattern
([stop (datum->syntax #'EXPRS 'stop)])
#'(let/ec stop
(while #t
. EXPRS))))
(module+ test
(require rackunit)
(check-equal? (let ([x 5])
(until (zero? x)
(set! x (- x 1)))
x) 0)
(check-equal? (let ([x 5])
(while (positive? x)
(set! x (- x 1)))
x) 0))