#lang racket

(define (modify-if trans code)
  ; locates every occurrence of an if expression in code and 
  ; applies the transform function to it.
  
  (if (and (list? code) (not (null? code)) (eq? 'if (first code)))
      ; found an (if ...) expr, transform the parts
      (trans (second code) (third code) (fourth code) )

      ; not an if, so if a ( ) then transform each of the parts
      ; otherwise leave alone
      (if (list? code) 
          (map (lambda (c) (modify-if trans c)) code)
          code)
      ))


(define c1 
  '(if true
      "c1-true"
      "c1-false"
      ))

(define c2
  '(if false
       (if (and true (if false true false))
           "c11"
           "c12"
           )
       "c21"
       ))

; transform (if c p q) into (if (not c) q p)
(define (trans-1 c p q)
  (list 'if (list 'not c) q p)
  )

(define (test1)
  (displayln (eval c1))
  (displayln (modify-if trans-1 c1))
  (displayln (eval (modify-if trans-1 c1)))
  (newline)
  (displayln (modify-if trans-1 c2))
  )

; (test1)