[plt-scheme] Defining structures

On Wed, Feb 18, 2009 at 4:26 PM, Todd O'Bryan <toddobryan at gmail.com> wrote:
> On Wed, Feb 18, 2009 at 1:52 PM, aditya shukla
> <adityashukla1983 at gmail.com> wrote:
>> A question that comes to mind if variables in scheme do not have type in
>> scheme thus can be say that
>>
>> (define a 9) -here a is a placeholder for a value whose tag is a number
>>
>>> (define a 'aditya)
>> define: cannot redefine name: a
>>
>>
>>
>> why can't we redefine a here?
>>
>>
>> Aditya
>
> Because you can only define something once. It doesn't have to do with
> the type--even if you tried to redefine a as another number, you'd
> still get the same error:
>
> (define a 1)
> (define a 2) <---- Scheme doesn't like this either
>

It really has to do with the restrictions imposed by the (student)
language you are using. One of the restrictions is that you can only
define a variable once. Full Scheme will allow you to redefine
anything (i.e. a variable, a function, etc.).

The question, Aditya, is why would you want to redefine a variable?
What sense does it make to define a variable more than once?

-- 

Cheers,

Marco