Yet Another Scheme Tutorial 第７章looping的一处代码错误

exercies 2 :
1. my-reverse that reverse the order of list items. (Function reverse is pre-defined.)
要求用尾递归写一个将列表逆序的函数。　
答案如下：

cat tail_reverse.scm
#! /usr/bin/env guile -s
!#

(define (my-reverse ls)
    (my-reverse-rec ls ()))

(define (my-reverse-rec ls0 ls1)
    (if (null? ls0)
        ls1
        (my-reverse rec (cdr ls0) (cons (car ls0) ls1))))

我实验了下这个代码会报错。

guile
GNU Guile 2.0.13
Copyright (C) 1995-2016 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)> (load "tail_reverse.scm")
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /usr/local/src/scheme/tail_reverse.scm
;;; WARNING: compilation of /usr/local/src/scheme/tail_reverse.scm failed:
;;; ERROR: Syntax error:
;;; unknown location: unexpected syntax in form ()
ice-9/boot-9.scm:703:29: In procedure map:
ice-9/boot-9.scm:703:29: Syntax error:
unknown location: unexpected syntax in form ()

Entering a new prompt.  Type `,bt' for a backtrace or `,q

代码修改下，将第六行中的()修改为空列表, '().

#! /usr/bin/env guile -s
!#

(define (my-reverse ls)
    (my-reverse-rec ls '())

(define (my-reverse-rec ls0 ls1)
    (if (null? ls0)
        ls1
        (my-reverse-rec (cdr ls0) (cons (car ls0) ls1))))

guile
(load "tail_reverse.scm")
,binding
my-reverse-rec          #>
my-reverse              #>
%module-public-interface #>
 (my-reverse (list 1 2 3 4 5))
$1 = (5 4 3 2 1)