Merge pull request #380 from reflex-frp/mapQueryT

Add mapQueryT

Author: Ericson2314

ChangeLog.md

@@ -1,5 +1,9 @@
 # Revision history for reflex
 
+## Unreleased
+
+* Add `Reflex.Query.Base.mapQueryT`. See that module for documentation
+
 ## 0.6.3
 
 * `Data.WeakBag.traverse` and `Data.FastWeakBag.traverse` have been deprecated.

src/Reflex/Query/Base.hs

@@ -16,6 +16,7 @@ module Reflex.Query.Base
   , mapQueryResult
   , dynWithQueryT
   , withQueryT
+  , mapQueryT
   ) where
 
 import Control.Applicative (liftA2)
@@ -287,6 +288,10 @@ withQueryT f a = do
     (fmapCheap (AdditivePatch . mapQuery f . unAdditivePatch) $ updatedIncremental q)
   return result
 
+-- | Maps a function over a 'QueryT' that can change the underlying monad
+mapQueryT :: (forall b. m b -> n b) -> QueryT t q m a -> QueryT t q n a
+mapQueryT f (QueryT a) = QueryT $ mapStateT (mapEventWriterT (mapReaderT f)) a
+
 -- | dynWithQueryT's (Dynamic t QueryMorphism) argument needs to be a group homomorphism at all times in order to behave correctly
 dynWithQueryT :: (MonadFix m, PostBuild t m, Group q, Additive q, Group q', Additive q', Query q')
            => Dynamic t (QueryMorphism q q')