INTERPRETER

#lang racket

;;; wersja binarna

(define (add-expr? e)
  (and (list? e)
       (= (length e) 3)
       (eq? (car e) '+)))

(define (const? e)
  (number? e))

(define (add-left e)
  (second e))

(define (add-right e)
  (third e))

(define (add-op e)
  (first e))

(define (op->proc o)
  (if (eq? o '+)
      +
      (error "WRONG OPERATOR -- ADD-EXPR" o)))

(define (eval e)
  (cond [(const? e) e]
        [(add-expr? e)
         ((op->proc (add-op e))
          (eval (add-left e))
          (eval (add-right e)))]))


;;; wersja na listach

(define (add-inf-expr? e)
  (and (list? e)
       (eq? (car e) '+)))

(define (add-inf-op e)
  (first e))

(define (add-inf-args e)
  (cdr e))

(define (eval-inf e)
  (cond [(const? e) e]
        [(add-inf-expr? e)
         (apply
          (op->proc (add-inf-op e))
          (map eval-inf (add-inf-args e)))]))