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9 points by kens 4758 days ago | link | parent

Is annotate a general mechanism, or specifically for defining macros? Is ellipsize supposed to limit its output to 80 characters or display at most 80 characters of the input? Is median of an even-length list supposed to return the lower of the middle two? Is cdar supposed to be missing? Is (type 3.0) supposed to be an int? Is support for complex numbers supposed to be in Arc? Is client-ip supposed to be there, or is it left over from something? Does afn stand for "anonymous fn"? What does "rfn" stand for?

These are all real questions that I've faced while trying to write documentation. Let me make it clear that these are not rhetorical questions; I'm more interested in getting actual answers than arguing about using the code as the spec.



7 points by pg 4758 days ago | link

The former; the latter; yes; yes; yes (for now); yes; the former (for now); anaphoric; recursive.

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6 points by parenthesis 4757 days ago | link

I've matched pg's replies up with the questions, to make this discussion easier to read:

annotate is a general mechanism

ellipsize is supposed to display at most 80 characters of the input

median of an even-length list is supposed to return the lower of the middle two

cdar is supposed to be missing

(type 3.0) is supposed to be an int (for now)

support for complex numbers is supposed to be in Arc

client-ip is supposed to be there (for now)

afn stands for "anaphoric function"

rfn stands for "recursive function"

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2 points by drewc 4749 days ago | link

But pg's was so much more concise! ;)

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4 points by eds 4757 days ago | link

>> 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.

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8 points by pg 4757 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 4757 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 4757 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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