Maybe you could just use the usual list processing functions on the
full file list? eg. a glob like "*.html" has an obvious implementation
with filter, and isSuffixOf.
I think it's a pretty good request. I can think of a few use cases
where this might come in handy...
I will probably implement regexes instead of globs, though -- because
Hakyll already depends on regex-pcre anyway.
I've just implemented  filename globbing. It should be fully
backward-compatible with the previous implementation. It's not on
Hackage yet because I want to do some more testing, but you can get it
from github  if you want.
Cool! It seems to work fine with the basic globs I've thrown at it.
I'll let you know if I run into any problems.
I think it'd be nice if patterns acted more like sets so you could
union/intersect/subtract them. This would allow more expressive policies
like "compile all non-markdown files using copyFile". But it looks like
this wouldn't make sense with current model of Patterns/Identifiers, so
I understand if you wouldn't want to implement it.
Keep up the great work!