Schemeのマクロ好き

gistfile1.sls

#!r6rs
(import (rnrs))

(define (iota-step k n s)
  (if (<= s 0) (assertion-violation 'iota "non-positive step" s))
  (cond ((> k n) '())
        (else    (cons k (iota-step (+ k s) n s)))))

(define-syntax iota
  (lambda (stx)
    (syntax-case stx (< <= by)
      [ (_      n     ) (syntax (iota-step 0 (- n 1) 1)) ]
      [ (_ k <  n     ) (syntax (iota-step k (- n 1) 1)) ]
      [ (_ k <  n by s) (syntax (iota-step k (- n 1) s)) ]
      [ (_ k <= n     ) (syntax (iota-step k    n    1)) ]
      [ (_ k <= n by s) (syntax (iota-step k    n    s)) ] )))


(define (println x) (display x) (newline))

(println (iota 5))            ; (0 1 2 3 4)
(println (iota 1 < 5))        ; (1 2 3 4)
(println (iota 1 <= 5))       ; (1 2 3 4 5)
(println (iota 0 < 10 by 2))  ; (0 2 4 6 8)