Hi Maciej,

Data.Generics.Schemes is now on the syb package, and I'm its maintainer. But I'm not so sure it is wise to start adding more traversal schemes of this form, since there might be many of them: if we include everywhereM', we certainly have to include the bottom-up everywhereM too. Then there are the possible Applicative variants, etc...

In general, since these traversal functions are small and everywhere and everywhere' already show the pattern of how to write them, maybe it's best that they are defined by the user, unless there is some general consensus that they would be widely useful.

Cheers,
Pedro

On Mon, Apr 12, 2010 at 20:56, Maciej Podgurski <maciej.podgurski@googlemail.com> wrote:

Hello,

as an analogue to everywhere', I suggest adding everywhereM' to Data.Generics.Schemes. The implementation would be

everywhereM' :: Monad m => GenericM m -> GenericM m
everywhereM' f x = do { x' <- f x;
gmapM (everywhereM' f) x' }

Best wishes,

Maciej
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