; exercise 2-4

(define (squeeze str c-or-s)
  (let ((dels (if (char? c-or-s)
                  (list c-or-s)
                  (string->list c-or-s))))
    (list->string
      (filter (lambda (c) (not (member c dels)))
              (string->list str)))))

(display (squeeze "Programming Praxis" #\P)) (newline)
(display (squeeze "Programming Praxis" "aeiou")) (newline)