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

Are you sure you ran exactly the same code and you were using exactly
the same version? At that level, there is no difference between the
two versions (ie, it is the same source code that implements cons
etc).

Robby

On Wed, Sep 16, 2009 at 11:15 PM, Ganesh Gunasegaran
<ganesh.gunas at gmail.com> wrote:
> Hi Jens,
>
> Thanks for the explanation. Couple of questions
>
> - The same code doesn't throw the mcar exception in Mac OSX version of
> DrScheme(4.2.1). The exception is thrown only in the linux version of
> DrScheme(4.2.1).
>
> - Even in the linux version of DrScheme, the exception is not thrown if I
> comment the unrelated letrec block.
>
> Even if shadowing occurs as you suggested, there is inconsistency across
> operating systems.
>
> Cheers,
> Ganesh Gunasegaran.
>
> #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))))))
>
>
> On 16-Sep-2009, at 11:29 PM, Jens Axel Søgaard wrote:
>
>> 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)
>>
>> One more thing:
>>
>> Since the entire rnrs/base-6 is required some functions from "scheme"
>> such as car, cdr, cons are shadowed by their bindings in rnrs/base-6.
>> In particular in rnrs the identifier car is bound to the same value
>> as the identifier mcar is bound to in "scheme'. That is, after the
>> require line, when you write "car" you are actually calling "mcar".
>>
>> This might we somewhat confusing, for new Scheme users, so
>> here is a practical advise:
>>
>> Stick either to the "scheme" language, and if you need a particular
>> function from rnrs use the documentation to figure out, what
>> is called in PLT Scheme (in 99% of the cases the names
>> are the same).
>>
>> --
>> Jens Axel Søgaard
>
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