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Code Select (define filter
(lambda (fn values)
"This function is a tail recursive implementation of the filter
function found in other Lisp dialect."
(let loop ((v values)
(rest '()))
;;; If there are items in v then CAR and CDR are saved; return
;;; rest after reversing.
;;;
;;; Checks if fn => #t -> add item to rest & repeat.
;;; => #f -> loop without adding item.
(if (pair? v)
(let ((item (car v))
(next (cdr v)))
(if (fn item)
(loop next (cons item rest))
(loop next rest)))
(reverse rest)))))Code Select (define filter
(lambda (fn values)
"This function is a tail recursive implementation of the filter function
found in other Lisp dialect."
(let loop ((v values)
(rest '()))
(let ((item (car v))
(next (cdr v))) ; Saves car and cdr for efficiency.
(if (fn item)
;; Add the current 'item to 'rest if 'fn returned #t, then continue
;; though the list. Return 'this AND 'rest revsered.
(if (pair? next)
(loop next (cons item rest))
(reverse (cons item rest)))
;; Don't add the 'item to the 'rest list but continue on though the
;; list.
(if (pair? next)
(loop next rest)
(reverse rest)))))))Code Select > (filter even? '(1 2 3 4 5 6 7))
(2 4 6)Code Select (defun explode (string)
(map 'list #'character string))
(defun explode2 (string)
(coerce string 'list))
(defun implode (object)
(coerce object 'string))Code Select
(define binary
(lambda (number)
"This function provides a simple generic front end to our
positive/negative binary functions."
(reverse
((if (> number 0)
positive-binary
negative-binary) number))))