[Pmwiki-users] Group specifier and free links (was Re: more --signature markup..)

[Christian Ridderström]

On Mon, 9 Feb 2004, Patrick R. Michaud wrote:

> On Mon, Feb 09, 2004 at 11:37:31PM +0100, Christian Ridderstr?m wrote:
> > 
> > Of course, writing that, I realize that putting '/' or a '.' can change
> > the interpretation drastically (e.g. Group/{{bla bla}}). OTOH, I've never
> > quite understood the reason for putting the group outside.
> 
> Well, WikiGroups predated FreeLinks by about a year, and when FreeLinks
> were added it was just deemed simpler to leave the Groups on the outside.

I see. Well, I'm not sure I'd want to change it now --- just mention that 
it *is* something that feels a bit weird. I remember having problems with 
it in the beginning, and I also remember questions being asked on the list 
about it.

> Besides, a FreeLink can start to look really funny with the group name
> inside:
> 
> {{My special group.my install|ation}}ed
> 
> {{My special group/my install|ation}}ed
> 
> Both link to MySpecialGroup.MyInstallation and one renders
> as "My special group.my installed" while the other renders as 
> "my installed". 

Doesn't that impliy new functionality? We can't enter group names like
that today AFAIK, and in general, I thought group names were more
restricted than the page names? I.e. in order for the above example to 
be consistent with todays markup they should be:

	{{MySpecialGroup.my install|ation}}ed
	{{MySpecialGroup/my install|ation}}ed

Although that doesn't look much better to me. OTOH, 

	MySpecialGroup/{{my install|ation}}ed

is still a bit funny looking to me.

> Plus, the FreeLinkPattern is already hairy enough [1] without trying to
> add groups to it, or figuring out if someone has specified a group on
> the inside or on the outside.

Ok, the implementation aspect again.

> 
> If you're willing to say that group names in FreeLinks should be displayed
> in their natural form (and not as the free link text), then it's
> conceivable to add these link patterns via an entry in $DoubleBrackets.
> But it will probably have a big impact on the WikiTrail code and other
> items that depend heavily on the current freelink patterns.

Ok. Maybe something for the future then, after checking with "normal"(*) 
users to see how they feel about it.

/Christian

(*) Normal, as in not having become used to the current syntax.

PS.

> 1.  For reference, the current $FreeLinkPattern is

Just for fun, I tried understanding it :-) Here's the original:
$FreeLinkPattern="{{(?>([[:alpha:]][[:alnum:]]*(?:(?:[\\s_]*|-)[[:alnum:]]+)*)(?:\\|((?:(?:[\\s_]*|-)[[:alnum:]])*))?)}}((?:-?[[:alnum:]]+)*)";

First I expand it so I can see the structure:
$FreeLinkPattern= "
{{
(?>
    (
        [[:alpha:]][[:alnum:]]*			
        (?:
            (?:[\\s_]*|-)
            [[:alnum:]]+
        )*					
    )
    (?:
        \\|
        (
            (?:
                (?:[\\s_]*|-)
                [[:alnum:]]
            )*
        )
    )?
)
}}
(
    (?:
        -?
        [[:alnum:]]+
    )*
)
";

And now I'll see if I can make it more compact by introducing 
subexpressions contained in variables:

$FreeLinkPattern= "
{{
(?>
    ( $tokenPattern $suffixPattern* )
    (?: $vbarChar 
        ( (?: $separatorPattern [[:alnum:]] )* )
    )?
)
}}
( (?: -? [[:alnum:]]+ )* )
";

$tokenPattern = "(?:[[:alpha:]][[:alnum:]]*)";
$separatorPattern = "(?:[\\s_]*|-)";
$suffixPattern = "(?:$separatorPattern[[:alnum:]]+)";
$vbarChar = "\\|";

I'll now describe the free link pattern using EBNF:

    free-link ::= '{{' token *suffix ?('|' *cut-text) '}}' *add-text
    token     ::= alpha *alnum
    suffix    ::= separator +alnum
    separator ::= +ext-ws | '-' | empty
    cut-text  ::= separator alnum
    add-text  ::= ?'-' +alnum
    ext-ws    ::= whitespace | '_'
    empty     ::= ()

Some questions:
* Why can <separator> allow *zero* or <ext-ws>, but only one '-'?
* Why allow only a single <alnum> in <cut-text>, but +<alnum> in <suffix>?

Would these rules work just as well?
    free-link ::= '{{' alpha *suffix ?('|' +suffix) '}}' *add-text
    suffix    ::= ?separator +alnum
    separator ::= '-' | +( whitespace | '_' )
    add-text  ::= ?'-' +alnum

-- 
Christian Ridderstr?m                           http://www.md.kth.se/~chr