Thread-Topic: \clist_length:N and \clist_nth:N
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Date:         Wed, 26 Jan 2011 13:19:02 +0000
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From: "Mittelbach, Frank" <frank.mittelbach@HP.COM>
Subject: Re: \clist_length:N and \clist_nth:N
To: LATEX-L@listserv.uni-heidelberg.de
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I don't have any issue with element or elt (having been exposed to lisp long time ago) but my feeling is that "length" is rather a good name for the concept, but then we should use it in other places too and get rid of elt_count there.

For _nth I think _element is ok, but I'm not so sure why _item would be bad. Don't see that there would be a conflict with other "items" of LaTeX. In fact it is the same concept, so why choose different names?

Frank

... written on the iPad 

Am 25.01.2011 um 10:37 schrieb "Robin Fairbairns" <Robin.Fairbairns@CL.CAM.AC.UK>:

> Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK> wrote:
> 
>> On 24/01/2011 14:01, Lars Hellström wrote:
>>> Isn't this "elt" an implementation detail for that type of list (various
>>> \@elt tokens in 2e come to mind), and thus something that should be kept
>>> internal rather than canonised in a public interface? The clean solution
>>> for *both* types of list is rather to use "length".
>> 
>> Seems reasonable: one would normally talk about 'a long list of things
>> to do', so lists to have 'length' :-)
> 
> in some ways of looking at a list, it has 'length'.
> 
> in plain english, i would say lists have "items" (or just "things")
> rather than "elements", but "item" is already heavily overloaded in
> the user's level latex-ese.  i don't have a problem with "element" (or
> "elt" in command names).
> 
>>> Moreover, I get a vague impression that the term `elt' is part of the
>>> pseudo-LISP heritage of LaTeX (emphasis on the "La"). If so, then that
>>> is IMHO another reason to avoid it, as that heritage is full of square
>>> pegs trying to fit in round holes.
>> 
>> Not being familiar with Lisp, I can only go on things like LaTeX2e's
>> \@cdr, etc., which have much more sensible names in expl3.
> 
> the "lisp heritage" is no more than simple use of some lisp names for
> some latex internal operations (e.g., car, cdr).  it's a long time (>40
> years) since i learned lisp, but i don't remember a special name for
> items in a lisp list.
> 
>>>> I didn't write "clist_nth" with a view of it being the permanent name,
>>>> but
>>>> now that I've written it I can't think of a (good) alternative. Any
>>>> thoughts?
>>> 
>>> I think the verb you're looking for is "index", i.e., the command name
>>> would be clist_index.
> 
> hmm.  index works, but i don't think it supports the "plain english" test.
> 
>> I'd imagine 'index' to be the other way around:
>> 
>>  \clist_index:Nn \l_some_clist { item } => Number
> 
> agreed.
> 
>> whereas what Will has implemented gives the 'entry', 'element', 'item'
>> or some such name. ('element' seems to be discouraged based on the first
>> part of your e-mail, so perhaps 'item' is better.)
> 
> i think element is as good as it gets, in this context.
> 
>>> first: Return index of first occurrence of a particular item within a
>>> clist,
>>>        or -1 (given 0-based indices) if the item does not occur therein.
>>> last:  Return index of last occurrence of a particular item within a
>>> clist,
>>>        or -1 (given 0-based indices) if the item does not occur therein.
>>>        (Note: Slightly trickier to implement.)
>> 
>> Both of these look relatively easy to do.
>> 
>>> range: Return a subrange of the clist, i.e., if \a_clist is "a,b,c,d" then
>>>        \clist_range:Nnn\a_clist{1}{2} returns "b,c". (I don't have an
>>>        opinion as to what might be the best sense of "return" in this
>>> case.)
>>> replace: Replace the material in a subrange of the clist by some other
>>>        clist material.
>> 
>> More tricky. Let's sort the others first :-)
> 
> robin
> 
> getting better every day.  very slightly.