Re: delete command weirdness

Peter Hildebrandt wrote:
> Nathaniel Calloway wrote:
> ...
> 
>> This is where my lack of understanding of lisp comes in. This is also
>> where my vernacular is lacking. If I can explain it in terms of
>> pointing, using my original example:
>>
>> testing -> (a . -> (b . -> (c . -> (d . -> nil)))
> 
> 
> Perfect.  So let's see:
> 
> Delete is a function, so it is passed the contents of testing, that is, 
> the whole list:
> 
> (a . -> (b . -> (c . -> (d . -> nil)))
> 
> Now, it can do with it whatever it wants.  If it wants to get rid of b, 
> it could take the first pointer and make it point to the c:
> 
>       +----------+
>       |          |
> (a . -+ (b . -> (c . -> (d . -> nil)))
> 
> Then the list becomes
> 
> (a . -> (c . -> (d . -> nil))
> 
> The symbol testing, however still points like this
> 
> testing
>    |
>    v
> (a . -> (c . -> (d . -> nil))
> 
> So, how do you want to get rid of the a? 

You know, it occurred to me that an implementation could copy the car 
and cdr of the second cons cell into the car and cdr of the first cons 
cell -- that would be cute.

Of course we are still not operating on "testing" itself, we just happen 
in this case to create that illusion via mutation.

I hope this confuses things. :)

kenny

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