Task

I need a regex to transform wiki markup surrounding words to html, * to <b> etc.

my problem is that */_ could be combined at word boundaries, see the following example

 DB<66> $_=$wiki; tf();tf();tf() ; print "'$wiki' \n=>\n'$_'" 
'_*one /two/*_ _*three /four/*_ _*five /six/*_'
=>
'<u><b>one <i>two</i></b></u> <u><b>three /four/</b></u> <u><b>five <i
+>six</i></b></u>'
 DB<67>
[download]

'_*one /two/*_ _*three /four/*_ _*five /six/*_'
=>
'one two three /four/ five six'

as you can see I have to run the tf() transformation thrice

 
  DB<40> %h = ( '*'=>'b', '/' => 'i' , '_' => 'u' ) 

  DB<59> sub tf { s{ $pre ([_*/]) (.*?) \2 $post}{$1<$h{$2}>$3</$h{$2}
+>$4}xg }

  DB<62> $pre = qr/(^|\s|>)/

  DB<63> $post = qr/($|\s|<)/    

  DB<65> $wiki='_*one /two/*_ _*three /four/*_ _*five /six/*_'
[download]

Question

Is there a way to make it a one-run transformation?

Trouble is that /g continues after the inserted replacement, here underline

I was experimenting with lookaround-assertions and \G and couldn't get it done.

Approaches

The only ways I can (theoretically) think of so far are

• to loop over /g in scalar context while (s///g) { ... } and to manipulate pos
• or to manipulate pos in an embedded Perl code (?{...})
• to call tf() recursively in the /e evaled replacement part

UPDATE:

I just noticed a bug, since four wasn't expanded.

&tf has to be better written with a lookbehind which doesn't consume the next whitespace

  DB<90> sub tf { s{ $pre ([_*/]) (.*?) \2 (?=$post)}{$1<$h{$2}>$3</$h
+{$2}>}xg }
[download]

I'll update an SSCCE soon.