Hi everyone, I'm repeatedly wondering why there are no `Functor`, `Foldable` and `Traversable` instances for `Expr`. Is this just by lack of motive? I could help there: I was looking for a function that would tell me if an expression mentions `makeStatic`. After spending some minutes searching in the code base, I decided to roll my own thing in `CoreUtils`. I really couldn't think about a good name, so I settled for `anyReferenceMatching :: (b -> Bool) -> Expr b -> Bool` and realized that I could generalize the function to `foldMapExpr :: Monoid m => (b -> m) -> Expr b -> m`. Occasionally this need pops up and I really want to avoid writing my own traversals over the syntax tree. So, would anyone object to a patch implementing these instances? Thanks Sebastian