makroting.rkt

#lang racket

(define-syntax-rule (run x)
  (begin (printf "> ~a~n" 'x)
         (printf "~a~n" x)))

(define-syntax-rule (baklengs a b c d)
  (d c b a))

(run (baklengs 2 1 #f if))

(define-syntax (foo stx)
  (syntax-case stx (bar)
    [(_ bar a) #'a]
    [(_ a b) #''(b a)]))

(run (foo bar 1))
(run (foo hest marsvin))

(define-syntax aiif
    (syntax-rules ()
      [(_ it condition then else)
       (let ([it condition])
         (if it then else))]))

(define (ganger n) (* n n))

(run (aiif eet (ganger 3) (* eet eet) eet))
(run (aiif eet #f (* eet eet) eet))

(define-syntax (aif stx)  
  (with-syntax ([it (datum->syntax stx 'it stx)])
    (syntax-case stx (aiif)
      [(_ condition then else)
       #'(aiif it condition then else)]
      [(_ condition then else . stuff)
       (raise-syntax-error #f "too much stuff:" stx #'stuff)])))

(run (aif (ganger 3) (* it it) it))

; ikke-kommenter linjen under for syntaks-feil
;(run (aif (ganger 3) (* it it) it asd qwe))