Add mergeWithThese.

haskellari · Mar 1, 2015 · 3c3dc27 · 3c3dc27
1 parent 7fe759f
commit 3c3dc27
Showing 1 changed file with 5 additions and 0 deletions.
diff --git a/Data/These.hs b/Data/These.hs
@@ -9,6 +9,7 @@ module Data.These (
                   , these
                   , fromThese
                   , mergeThese
+                  , mergeTheseWith
 
                   -- * Traversals
                   , here, there
@@ -85,6 +86,10 @@ fromThese _ _ (These a x) = (a, x)
 mergeThese :: (a -> a -> a) -> These a a -> a
 mergeThese = these id id
 
+-- | BiMap and coalesce results with the provided operation.
+mergeTheseWith :: (a -> c) -> (b -> c) -> (c -> c -> c) -> These a b -> c
+mergeTheseWith f g op t = mergeThese op $ mapThese f g t
+
 
 -- | A @Traversal@ of the first half of a 'These', suitable for use with @Control.Lens@.
 here :: (Applicative f) => (a -> f b) -> These a t -> f (These b t)