[xmonad] Property vs Query Bool

[Konstantin Sobolev]

Hello

I'm trying to implement my own LayoutClass which mixes the ideas of IM
and CombineTwo. It has to contain some predicate as a part of it's
state, which will tell where to put new windows.
As I see IM uses WindowProperties for this purpose, but I wouldn't
like to use it for 2 reasons:
1. Property essentially duplicates Query Bool.
2. Property isn't flexible enough. For instance, I can't match a
window by title substring, while I can easily do it with Query.
However, there's one problem (and I guess that's why Property was
introduced): Query doesn't derive Read and Show, and as far as I
understand it's not so easy to implement them.
So what should I use, Query Bool with empty (Read, Show)
implementations, losing state between restarts; or Property losing
flexibility that I'd like to have?

Thanks.