Guided Practice 5.3: S-expressions

Design the following functions:

;; characters-in-sexp  : Sexp -> Number
;; characters-in-sexps : SexpList -> Number
;; RETURNS: the total number of characters in the strings in the given
;; Sexp or SexpList
;; EXAMPLE/TEST:
(begin-for-test
  (check-equal?
   (characters-in-sexp
    (list "alice" 
          (list (list "alice" "bob") "carole")
          "dave"))
   23)

;; subst : Sexp String String -> Sexp
;; GIVEN: a Sexp and two strings, old and new
;; RETURNS: an Sexp just like the given one, except that
;; all instances of old are changed to new.
;; EXAMPLE/TEST:
(begin-for-test
  (check-equal? 
    (subst
      (list "alice" 
        (list (list "alice" "bob") "dave") 
        "eve"
        "bob")
      "bob"
      "ted")
    (list "alice" 
      (list (list "alice" "ted") "dave") 
      "eve"
      "ted")))

[ANSWER]

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Last modified: Fri Aug 11 15:04:33 Eastern Daylight Time 2017