Add monadic query functions

[HaskellZhangSong]

This commit adds following monadic query functions in issue #35:

everythingButM :: forall m r. Monad m => (r -> r -> r) -> GenericQ (m (r, Bool)) -> GenericQ (m r)
everythingMButM :: forall m r. Monad m => (m r -> m r -> m r) -> GenericQ (m (r, Bool)) -> GenericQ (m r)
everythingWithContextM :: forall m s r. Monad m => s -> (r -> r -> r) -> GenericQ (m (s -> (r, s))) -> GenericQ (m r)
everythingMWithContextM :: forall m s r. Monad m => s -> (m r -> m r -> m r) -> GenericQ (m (s -> (r, s))) -> GenericQ (m r)

which make query with unavoidable monadic query easier.

[sergv]

@HaskellZhangSong I think everythingButM and everythingMButM are reasonable generalisations of what's already in the library (although I'd probably consider having GenericQ (m (Maybe r)) instead of GenericQ (m (r, Bool)) when designing from scratch) but signatures of everythingWithContextM and everythingMWithContextM look convoluted. Why can't the context in there (the s -> (..., s) bit) be passed a part of the monad?

[HaskellZhangSong]

I did not think this very carefully. I just extend everythingBut by lifting (r, Bool) to m (r, Bool). Similarly applied to everythingWithContext function too.

Why can't the context in there (the s -> (..., s) bit) be passed a part of the monad?

I am not quite sure about how and what exactly you mean. Do you mean to combine m with a state monad? Could you show the code? Here, I just think the m in (m r -> m r -> m r) should be coherent with the m in (m (s -> (r, s)))

Thanks

[sergv]

I was thinking about something along the lines

everythingMWithContextM :: forall n s r. Monad n => (StateT s n r -> StateT s n r -> StateT s n r) -> GenericQ (StateT s n r)) -> GenericQ (StateT s n r)

I.e. to obtain everythingMWithContextM the user instantiates already defined everything funsction.

[HaskellZhangSong]

I think this looks more complicated and need to bring mtl library into syb.

[sergv]

syb doesn't have to depend on mtl (transformers would be enough) - user can instantiate existing functions themselves in their package.