dotimes, syntax, scheme

dotimes.scm

;; dotimes

(define-syntax dotimes
  (syntax-rules ()
    ((_ n body ...)
     (do ((i n (- i 1)))
         ((not (< 0 i)))
       body ...))))

(dotimes 5
  (display "hello")
  (print "world"))
;; helloworld
;; helloworld
;; helloworld
;; helloworld
;; helloworld
;; #t

(define-syntax dotimes
  (syntax-rules ()
    ((_ n body ...)
     (let loop ((i n))
       (when (< 0 i)
         body ...
         (loop (- i 1)))))))

(dotimes 5
  (print "H")
  (print "l")
  (print "l")
  (print "o"))
;; H
;; l
;; l
;; o
;; H
;; l
;; l
;; o
;; H
;; l
;; l
;; o
;; H
;; l
;; l
;; o
;; H
;; l
;; l
;; o
;; #<undef>

expanded-dotimes.scm

;; dotimes

(define-syntax dotimes
  (syntax-rules ()
    ((_ n body ...)
     (let loop ((i n))
       (when (< 0 i)
         body ...
         (loop (- i 1)))))))

(dotimes 5 (print 1))

(define i 10)
(dotimes 5 (print (set! i (+ i 1))))
;; 11
;; 12
;; 13
;; 14
;; 15


(macroexpand-1 '(dotimes 5 (print (set! i (+ i 1)))))
;; (#<identifier user#let> #0=#<identifier user#loop>
;;               ((#1=#<identifier user#i> 5))
;;               (#<identifier user#when>
;;                             (#<identifier user#<> 0 #1#)
;;                             (print (set! i (+ i 1)))
;;                             (#0# (#<identifier user#-> #1# 1))))