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+;"sc4opt.scm" Implementation of optional Scheme^4 functions for IEEE Scheme
+;Copyright (C) 1991, 1993 Aubrey Jaffer.
+;
+;Permission to copy this software, to redistribute it, and to use it
+;for any purpose is granted, subject to the following restrictions and
+;understandings.
+;
+;1.  Any copy made of this software must include this copyright notice
+;in full.
+;
+;2.  I have made no warrantee or representation that the operation of
+;this software will be error-free, and I am under no obligation to
+;provide any services, by way of maintenance, update, or otherwise.
+;
+;3.  In conjunction with products arising from the use of this
+;material, there shall be no use of my name in any advertising,
+;promotional, or sales literature without prior written consent in
+;each case.
+
+;;; Some of these functions may be already defined in your Scheme.
+;;; Comment out those definitions for functions which are already defined.
+
+;;; This code conforms to: William Clinger and Jonathan Rees, editors.
+;;; Revised^4 Report on the Algorithmic Language Scheme.
+
+(define (list-tail l p)
+  (if (< p 1) l (list-tail (cdr l) (- p 1))))
+
+(define (string->list s)
+  (do ((i (- (string-length s) 1) (- i 1))
+       (l '() (cons (string-ref s i) l)))
+      ((< i 0) l)))
+
+(define (list->string l) (apply string l))
+
+(define string-copy string-append)
+
+(define (string-fill! s obj)
+  (do ((i (- (string-length s) 1) (- i 1)))
+      ((< i 0))
+      (string-set! s i obj)))
+
+(define (list->vector l) (apply vector l))
+
+(define (vector->list s)
+  (do ((i (- (vector-length s) 1) (- i 1))
+       (l '() (cons (vector-ref s i) l)))
+      ((< i 0) l)))
+
+(define (vector-fill! s obj)
+  (do ((i (- (vector-length s) 1) (- i 1)))
+      ((< i 0))
+      (vector-set! s i obj)))