Arc Forum | >> Is cdar supposed to be missing?> yesWasn't the point keeping the ...

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4 points by eds 6486 days ago | link | parent

>> Is cdar supposed to be missing?

> yes

Wasn't the point keeping the names car and cdr so you can compose them? (I remember reading such in one of pg's essays.) Then it seems to me to take full advantage of that you need to provide those names for use.

I don't think it is unreasonable to do the following, but it is currently not provided in Arc:

arc> (cdar '((1 2 3) (4 5 6))) Error: "reference to undefined identifier: _cdar"

Maybe this is just me missing CL's four levels of composition of car and cdr.

8 points by pg 6486 days ago | link

I didn't mean Arc will never have cdar. But to avoid having a language designed according to arbitrary rules rather than the actual demands of the task, I've been trying to be disciplined about not adding operators till I need them.

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5 points by parenthesis 6486 days ago | link

I suppose you can cdr:car .

On the one hand, it does feel like all the c....r s should be there.

On the other hand, I think cadr is pretty much the only one I ever actually use; and it is there.

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2 points by drcode 6486 days ago | link

I noticed this contradiction, too... :) If we're not going to use c[ad]r composability, why not just use unique, easily distinguishable names for all of these that don't compose:

 car --> hd
 cdr --> tl
 caar --> inner
 cddr --> skip2
 cadr --> second

...or something like that. Unique names would reduce errors.

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