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

You might also just get rid of the line:

  (require rnrs/base-6)

It doesn't seem to be doing anything useful (unless I'm missing something)?

2009/9/16 Jens Axel Søgaard <jensaxel at soegaard.net>:
> [sent privately too by accident]
>
> 2009/9/16 Ganesh Gunasegaran <ganesh.gunas at gmail.com>:
>> 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)
>> --------------------------------------------------------------------------------------------------------------------------------
>
>> Am I missing something?
>
> There are two concepts of pairs in PLT Scheme: immutable and mutable pairs.
> The "scheme" language use immutable pairs, and the rnrs languages use
> mutable ones.
> Since the language chosen in this source file is Scheme, the expression '(1 2 3)
> will expand to (quote (1 2 3)) which again will expand to
>  (immutable-cons 1 (immutable-cons 2 (immutable-cons 3 null))) .
> Since functions such as mcar from rnrs expect mutable pairs, you'll
> get an error.
>
> Instead of '(1 2 3) try (mcons 1 (mcons 2 (mcons 3 null))).
>
> After thought: Is there an "mutable quote" mquote available somewhere?
>
> --
> Jens Axel Søgaard
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