chibi-scheme/lib/srfi/1/deletion.scm

;; deletion.scm -- list deletion utilities
;; Copyright (c) 2009-2012 Alex Shinn.  All rights reserved.
;; BSD-style license: http://synthcode.com/license.txt

(define (delete x ls . o)
  (let ((eq (if (pair? o) (car o) equal?)))
    (if (eq? eq eq?)
        (let lp ((ls ls) (rev '())) ;; fast path for delq
          (let ((tail (memq x ls)))
            (if tail
                (lp (cdr tail) (take-up-to-reverse ls tail rev))
                (if (pair? rev) (append-reverse! rev ls) ls))))
        (remove (lambda (y) (eq x y)) ls))))

(define delete! delete)

(define (delete-duplicates ls . o)
  (let ((eq (if (pair? o) (car o) equal?)))
    (let lp ((ls ls) (res '()))
      (if (pair? ls)
          (lp (cdr ls) (if (member (car ls) res eq) res (cons (car ls) res)))
          (reverse! res)))))

(define delete-duplicates! delete-duplicates)