Re: [Jscheme-user] Minor nuisance/inconsistency

[Robert J. B. <ru...@bb...>]

Tim,
I am comfortable with second and third showing an error -- their 
intended semantics is to treat the sequence of linked pairs as a linear 
structure and get the numbered element. It is an "implementation detail" 
that second is the same as cadr. I also support having symbolic methods 
fourth, ... tenth -- I keep getting burned by their absense.
Thanks,
Rusty


Timothy Hickey wrote:

>
> On Friday, March 7, 2003, at 11:20 AM, Robert J. Bobrow wrote:
>
>> Folks,
>> I  would expect that (cadr x) and (car (cdr x)) would behave 
>> identically in all circumstances. Yet I find that car and cdr behave 
>> like Common Lisp and return '() when given '() as an argument (I like 
>> this, personnaly) and cadr throws an exception when handed '();
>>
>> I think the inconsistency is annoying -- I really prefer not to have 
>> (car (cdr x)) in my code.
>
> I've fixed that inconsistency, cadr and caddr were treated differently 
> from all other cadadars
>
> I have however kept that behavior for second and third.
> So (second '(a)) --> error
>       (cadr '(a)) --> ()
> Perhaps it would be better to have second and third adhere to the same 
> semantics of cadr and caddr,
> but in a way it makes sense for second/third to give errors if the 
> lists are too short....
> I'd also like to add third, fourth, fifth, .... up to tenth or so....
>
> What do you think?
> ---Tim---
>
>