ex_2_54.clj

(ns sicp.chapter-2.part-3.ex-2-54)

; Exercise 2.54
;
; Two lists are said to be equal? if they contain equal elements arranged in the same order.
; For example,
;
; (equal? '(this is a list)
;         '(this is a list))
;
; is true, but
;
; (equal? '(this is a list)
;         '(this (is a) list))
; is false.
;
; To be more precise, we can define equal? recursively in terms of the basic eq?
; equality of symbols by saying that a and b are equal? if they are both symbols and the
; symbols are eq?, or if they are both lists such that (car a) is equal? to (car b) and (cdr a)
; is equal? to (cdr b). Using this idea, implement equal? as a procedure.

(defn equal?
  [a b]
  (cond
    (and (symbol? a) (symbol? b)) (= a b)
    (and (list? a) (list? b))
    (and (= (count a) (count b)) (every? true? (map equal? a b)))
    :else false))