[plt-scheme] Side effect requiring rnrs/base-6?

Hi All,

I am very new to Scheme

What is wrong with the following code?

--------------------------------------------------------------------------------------------------------------------------------
#lang scheme
(require rnrs/base-6)
(letrec ([my-sum (lambda (l)
             (if (null? l)
                 0
                 (+ (car l) (my-sum (cdr l)))))])
  (my-sum '(1 2 3 4)))
(define my-sum
  (lambda (l)
    (if (null? l)
        0
        (+ (car l) (my-sum (cdr l))))))

OUTPUT
Welcome to DrScheme, version 4.2.1 [3m].
Language: Module; memory limit: 128 megabytes.
10
> (my-sum '(1 2 3))
. . mcar: expects argument of type <mutable-pair>; given (1 2 3)
--------------------------------------------------------------------------------------------------------------------------------


If I comment (require rnrs/base-6) or the letrec block the code works as
intended
--------------------------------------------------------------------------------------------------------------------------------
#lang scheme
;(require rnrs/base-6)
(letrec ([my-sum (lambda (l)
             (if (null? l)
                 0
                 (+ (car l) (my-sum (cdr l)))))])
  (my-sum '(1 2 3 4)))
(define my-sum
  (lambda (l)
    (if (null? l)
        0
        (+ (car l) (my-sum (cdr l))))))

OUTPUT
Welcome to DrScheme, version 4.2.1 [3m].
Language: Module; memory limit: 128 megabytes.
10
> (my-sum '(1 2 3))
6
--------------------------------------------------------------------------------------------------------------------------------
#lang scheme
(require rnrs/base-6)
#|(letrec ([my-sum (lambda (l)
             (if (null? l)
                 0
                 (+ (car l) (my-sum (cdr l)))))])
  (my-sum '(1 2 3 4)))|#
(define my-sum
  (lambda (l)
    (if (null? l)
        0
        (+ (car l) (my-sum (cdr l))))))

OUTPUT
Welcome to DrScheme, version 4.2.1 [3m].
Language: Module; memory limit: 128 megabytes.
> (my-sum '(1 2 3))
6
--------------------------------------------------------------------------------------------------------------------------------

Am I missing something?

Cheers,
Ganesh Gunasegaran
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