Getting fill-paragraph to play nice with javadoc-like comments

[joakim.harsman@gmail.com]

I'm writing a major mode for an APL dialect I use at work. I've gotten
basic font locking to work, and after setting comment-start and
comment-start-skip, comment/uncomment region and fill paragraph also
work.

However, comment blocks often contain javadoc style comments and i
would like fill-paragraph to avoid gluing together lines starting
with such commands.

If I have this (\ instead of javadoc @):

# This is a comment that is long and should be wrapped.
# \arg Description of argument
# \ret Description of return value

M-q gives me:

# This is a comment that is long and
# should be wrapped. \arg Description
# of argument \ret Description of
# return value

But I want:

# This is a comment that is long and
# should be wrapped.
# \arg Description of argument
# \ret Description of return value

I've tried setting up paragraph-start and paragraph-separate to
appropriate values, but fill-paragraph still doesn't work inside a
comment block. If I remove the comment markers, M-q works as I want
to, so the regexp I use for paragraph-start seems to work.

Any ideas? Do I have to write a custom fill-paragraph for my major
mode? cc-mode has one that handles cases like this, but it's really
complex, I'd like to avoid it if possible.

I also tried setting fill-nobreak-predicate to an appropriate
function, but that didn't seem to have any effect at all.