Re: missing space after \date[] (was: printing the current date)

[Hans Hagen <j.hagen@xs4all.nl>]

On 3/13/2021 12:10 AM, Peter Münster wrote:
> On Wed, Jan 27 2021, Wolfgang Schuster wrote:
> 
>> When not all optional arguments are used the space after the last
>> given argument is gobbled. This was normal behavior for a long time
>> until you changed the code in MkIV to keep them.
> 
> Hi,
> 
> What does that mean? Is that going to be changed?
> How should \date[] be used now in the text?
> For now, I do it like "bla \date[d=3]\ bla".
> Is there a nicer way?
> 
> TIA for any hints,
The problem with an interface with optional arguments is that it has to 
look ahead. There are actually some macros that use this feature to get 
rid of upcoming spaces (picking up two optional arguments where one is 
needed). So, no matter what solution is chosen: push back a space or 
not, it has some unpredictable character.

This is why I always am explicit, as in \date[d=3]\ bla because no 
matter what happens bvehind the screens, the \ terminates the argument 
check so it will stay. (I admit that i'm mnore often bitten by the 
pushed back one than the gobbled one so i make it a habit to be explicit 
about spaces, like like i use \removeunwantedspaces when i'm not sure
when there can be spaces that crept in).

We can of course in lmtx bring back the 'push back a space' behaviour 
but we then also introduce some fuzzyness. Now we have "we scan upto n 
arguments and gobble spaces when doing so".

Btw, there is also another aspect: when looking for optional arguments 
the next token gets looked at and that one can be in an upcoming macro 
or content.

\startfoo[a][b]
    content
\stopfoo

\startfoo[a]
    [ that starts content
\stopfoo

so sometimes one needs

\startfoo[a]
    \relax [ that starts content
\stopfoo

to abort the scanning.

Hans

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