add Data.Foldable.{for_,forM_} and Data.Traversable.{for,forM}

[ghc-base.git] / Data / Traversable.hs

diff --git a/Data/Traversable.hs b/Data/Traversable.hs
index 14edb79..c2c6033 100644 (file)
--- a/Data/Traversable.hs
+++ b/Data/Traversable.hs
@@ -29,6 +29,8 @@
 
 module Data.Traversable (
        Traversable(..),
+       for,
+       forM,
        fmapDefault,
        foldMapDefault,
        ) where
@@ -106,6 +108,16 @@ instance Ix i => Traversable (Array i) where
 
 -- general functions
 
+-- | 'for' is 'traverse' with its arguments flipped.
+for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b)
+{-# INLINE for #-}
+for = flip traverse
+
+-- | 'forM' is 'mapM' with its arguments flipped.
+forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)
+{-# INLINE forM #-}
+forM = flip mapM
+
 -- | This function may be used as a value for `fmap` in a `Functor` instance.
 fmapDefault :: Traversable t => (a -> b) -> t a -> t b
 fmapDefault f = getId . traverse (Id . f)