diff options
| -rw-r--r-- | libraries/base/Control/Applicative.hs | 5 | ||||
| -rw-r--r-- | libraries/base/Data/Traversable.hs | 7 |
2 files changed, 9 insertions, 3 deletions
diff --git a/libraries/base/Control/Applicative.hs b/libraries/base/Control/Applicative.hs index 39b6466b53..a2f342f83f 100644 --- a/libraries/base/Control/Applicative.hs +++ b/libraries/base/Control/Applicative.hs @@ -122,8 +122,9 @@ instance (ArrowZero a, ArrowPlus a) => Alternative (WrappedArrow a b) where -- @f '<$>' 'ZipList' xs1 '<*>' ... '<*>' 'ZipList' xsn = 'ZipList' (zipWithn f xs1 ... xsn)@ -- newtype ZipList a = ZipList { getZipList :: [a] } - deriving ( Show, Eq, Ord, Read, Functor, Foldable - , Generic, Generic1) + deriving ( Show, Eq, Ord, Read, Functor + , Foldable, Generic, Generic1) +-- See Data.Traversable for Traversabel instance due to import loops instance Applicative ZipList where pure x = ZipList (repeat x) diff --git a/libraries/base/Data/Traversable.hs b/libraries/base/Data/Traversable.hs index 535db00125..81e639cf37 100644 --- a/libraries/base/Data/Traversable.hs +++ b/libraries/base/Data/Traversable.hs @@ -46,7 +46,9 @@ module Data.Traversable ( foldMapDefault, ) where -import Control.Applicative ( Const(..) ) +-- It is convenient to use 'Const' here but this means we must +-- define a few instances here which really belong in Control.Applicative +import Control.Applicative ( Const(..), ZipList(..) ) import Data.Either ( Either(..) ) import Data.Foldable ( Foldable ) import Data.Functor @@ -217,6 +219,9 @@ instance Traversable First where instance Traversable Last where traverse f (Last x) = Last <$> traverse f x +instance Traversable ZipList where + traverse f (ZipList x) = ZipList <$> traverse f x + -- general functions -- | 'for' is 'traverse' with its arguments flipped. For a version |