Sometimes you want to match a page only if it has certain properties. The use case I have in mind is this: show me all the pages that have children. You can't do that with a pagespec, so I created a plugin that adds some pagespec functions.

match_relative(blah) will match a page x if a pagespec from x would match blah. This is only actually useful with relative pagespecs.

match_has_child(blah) will match a child if it has a descendant named blah. If blah is empty, any child will match.

So if I have:

• foo
• foo/blah
• foo/bar
• foo/bar/blah
• foo/bar/bahoo
• foo/baz
• foo/baz/goo
• foo/baz/goo/blah

A pagespec match_relative(./blah) will match foo/bar/bahoo, because a pagespec of ./blah from bahoo would match foo/bar/blah. A pagespec of match_has_child(blah) would match foo, foo/bar, foo/baz, and foo/baz/goo.

Note that if you try to inline */blah you will match foo/blah, foo/bar/blah, and foo/baz/goo/blah -- that is, the blah pages themselves rather than any relatives of theirs.

This patch is useful for (among other things) constructing blogging systems where leaf nodes are organized hierarchically; using has_child, you can inline only leaf nodes and ignore "intermediate" nodes. match_relative can be used recursively to match properties of arbitrary complexity: "show me all the pages who have children called foo that have children called blah". I'm not sure what use it is, though.

You can see the patch in action at http://ikidev.betacantrips.com/conditionaltest/, so named because I had hoped that something in conditional.pm could help me. I know the name "relative" sucks, feel free to come up with a better one. --Ethan

diff -urNX ignorepats ikiwiki/IkiWiki/Plugin/relative.pm ikidev/IkiWiki/Plugin/relative.pm
--- ikiwiki/IkiWiki/Plugin/relative.pm  1969-12-31 16:00:00.000000000 -0800
+++ ikidev/IkiWiki/Plugin/relative.pm   2007-07-26 21:48:10.642686000 -0700
@@ -0,0 +1,39 @@
+#!/usr/bin/perl
+# relative.pm: support for pagespecs on possible matches
+package IkiWiki::Plugin::relative;
+
+use warnings;
+use strict;
+use IkiWiki 2.00;
+
+package IkiWiki::PageSpec;
+
+sub match_relative($$;@) {
+   my $parent = shift;
+   my $spec = shift;
+   my %params = @_;
+
+   foreach my $page (keys %IkiWiki::pagesources) {
+       next if $page eq $parent;
+       if (IkiWiki::pagespec_match($page, $spec, location => $parent)) {
+           return IkiWiki::SuccessReason->new("$parent can match $spec against $page");
+       }
+   }
+   return IkiWiki::FailReason->new("$parent can't match $spec against anything");
+}
+
+sub match_has_child($$;@) {
+   my $page = shift;
+   my $childname = shift;
+   my $spec;
+   if ($childname) {
+       $spec = "$page/$childname or $page/*/$childname";
+   }
+   else {
+       $spec = "$page/*";
+   }
+
+   return match_relative($page, $spec, @_);
+}
+
+1

This looks really interesting. It reminds me of XPath and its conditionals. Those might actually work well adapted to pagespecs. For instance, to write "match any page with a child blah", you could just write [blah] , or if you don't want to use relative-by-default in the conditionals, [./blah]. -- JoshTriplett

And it ?also reminds me of description logics: of course, given the relation subpage one could write a description-logic-style formula which would define the class of pages that are ("existentially") in a given relation (subpage or inverse(subpage)*subpage) to a certain other class of pages (e.g., named "blah") ("existentially" means there must exist a page, e.g., named "blah", which is in the given relation to the candidate).

Probably the model behind XPath is similar (although I don't know enough to say this definitely).--Ivan Z.