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Date:         Thu, 1 Sep 2011 16:07:07 +0200
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From: Philipp Stephani <p.stephani2@GOOGLEMAIL.COM>
Subject: Re: Internal equivalent of \providecommand?
To: LATEX-L@listserv.uni-heidelberg.de
In-Reply-To:  <fqvtzpmiulpq.dlg@nililand.de>
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Status: R

2011/9/1 Ulrike Fischer <news3@nililand.de>:
> Am Thu, 1 Sep 2011 13:08:32 +0100 schrieb Joseph Wright:
>
>> On 01/09/2011 11:57, Ulrike Fischer wrote:
>>> Is there an expl3 equivalent for a \providecommand?
>>>
>>> I could do
>>>
>>> \cs_if_free:NT \mycommand {\cs_set:Npn \mycommand {...}}
>>>
>>> but I don't find it very elegant to have to type \mycommand twice.
>
>> At the code level, the answer is 'no'. Within a module, we'd expect all
>> functions to be well-defined: if they 'might' be needed, they should
>> exist. (See for example the fact that a lot of internal aux functions
>> are created simply to mark the name as taken.)
>
>> Now, there is the reality that LaTeX2e stuff is often not so
>> well-designed and does sometime rely on 'might exist' functions. There,
>> I'm afraid the construct you've pointed to is the way to go.
>
>
> Well my command (it is more a variable so \tl_set would perhaps be
> more correct) must exist and that's why I'm using \providecommand:
> To make sure *that* is exists. I'm not relying on a "might exist"
> command but try to ensure that it is a "does exist" command.
>
> The problem is that it must exist in various encoding definitions
> files for fontenc, in the sty (chessfss) and that its "value" can be
> set/changed by the user -- which means that I have no control over
> the location where the default value should be set. I have to set it
> in various places in such a way that it doesn't overwrite user
> settings.

Wouldn't it be more appropriate to use a key-value option with default
value then?