Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: cc650b4b by Andrew Lelechenko at 2025-07-17T12:30:24-04:00 Add Data.List.NonEmpty.mapMaybe As per https://github.com/haskell/core-libraries-committee/issues/337 - - - - - 6 changed files: - libraries/base/changelog.md - libraries/base/src/Data/List/NonEmpty.hs - testsuite/tests/interface-stability/base-exports.stdout - testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs - testsuite/tests/interface-stability/base-exports.stdout-mingw32 - testsuite/tests/interface-stability/base-exports.stdout-ws-32 Changes: ===================================== libraries/base/changelog.md ===================================== @@ -1,5 +1,8 @@ # Changelog for [`base` package](http://hackage.haskell.org/package/base) +## 4.23.0.0 *TBA* + * Add `Data.List.NonEmpty.mapMaybe`. ([CLC proposal #337](https://github.com/haskell/core-libraries-committee/issues/337)) + ## 4.22.0.0 *TBA* * Define `displayException` of `SomeAsyncException` to unwrap the exception. ([CLC proposal #309](https://github.com/haskell/core-libraries-committee/issues/309)) ===================================== libraries/base/src/Data/List/NonEmpty.hs ===================================== @@ -78,6 +78,7 @@ module Data.List.NonEmpty ( , span -- :: (a -> Bool) -> NonEmpty a -> ([a], [a]) , break -- :: (a -> Bool) -> NonEmpty a -> ([a], [a]) , filter -- :: (a -> Bool) -> NonEmpty a -> [a] + , mapMaybe -- :: (a -> Maybe b) -> NonEmpty a -> [b] , partition -- :: (a -> Bool) -> NonEmpty a -> ([a],[a]) , group -- :: (Foldable f, Eq a) => f a -> [NonEmpty a] , groupBy -- :: Foldable f => (a -> a -> Bool) -> f a -> [NonEmpty a] @@ -118,6 +119,7 @@ import qualified Prelude import Control.Applicative (Applicative (..), Alternative (many)) import qualified Data.List as List +import qualified Data.Maybe as List (mapMaybe) import GHC.Internal.Data.Foldable hiding (length, toList) import qualified GHC.Internal.Data.Foldable as Foldable import GHC.Internal.Data.Function (on) @@ -442,6 +444,14 @@ break p = span (not . p) filter :: (a -> Bool) -> NonEmpty a -> [a] filter p = List.filter p . toList +-- | The 'mapMaybe' function is a version of 'map' which can throw +-- out elements. In particular, the functional argument returns +-- something of type @'Maybe' b@. If this is 'Nothing', no element +-- is added on to the result list. If it is @'Just' b@, then @b@ is +-- included in the result list. +mapMaybe :: (a -> Maybe b) -> NonEmpty a -> [b] +mapMaybe f (x :| xs) = maybe id (:) (f x) $ List.mapMaybe f xs + -- | The 'partition' function takes a predicate @p@ and a stream -- @xs@, and returns a pair of lists. The first list corresponds to the -- elements of @xs@ for which @p@ holds; the second corresponds to the ===================================== testsuite/tests/interface-stability/base-exports.stdout ===================================== @@ -1467,6 +1467,7 @@ module Data.List.NonEmpty where last :: forall a. NonEmpty a -> a length :: forall a. NonEmpty a -> GHC.Internal.Types.Int map :: forall a b. (a -> b) -> NonEmpty a -> NonEmpty b + mapMaybe :: forall a b. (a -> GHC.Internal.Maybe.Maybe b) -> NonEmpty a -> [b] nonEmpty :: forall a. [a] -> GHC.Internal.Maybe.Maybe (NonEmpty a) nub :: forall a. GHC.Internal.Classes.Eq a => NonEmpty a -> NonEmpty a nubBy :: forall a. (a -> a -> GHC.Internal.Types.Bool) -> NonEmpty a -> NonEmpty a ===================================== testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs ===================================== @@ -1467,6 +1467,7 @@ module Data.List.NonEmpty where last :: forall a. NonEmpty a -> a length :: forall a. NonEmpty a -> GHC.Internal.Types.Int map :: forall a b. (a -> b) -> NonEmpty a -> NonEmpty b + mapMaybe :: forall a b. (a -> GHC.Internal.Maybe.Maybe b) -> NonEmpty a -> [b] nonEmpty :: forall a. [a] -> GHC.Internal.Maybe.Maybe (NonEmpty a) nub :: forall a. GHC.Internal.Classes.Eq a => NonEmpty a -> NonEmpty a nubBy :: forall a. (a -> a -> GHC.Internal.Types.Bool) -> NonEmpty a -> NonEmpty a ===================================== testsuite/tests/interface-stability/base-exports.stdout-mingw32 ===================================== @@ -1467,6 +1467,7 @@ module Data.List.NonEmpty where last :: forall a. NonEmpty a -> a length :: forall a. NonEmpty a -> GHC.Internal.Types.Int map :: forall a b. (a -> b) -> NonEmpty a -> NonEmpty b + mapMaybe :: forall a b. (a -> GHC.Internal.Maybe.Maybe b) -> NonEmpty a -> [b] nonEmpty :: forall a. [a] -> GHC.Internal.Maybe.Maybe (NonEmpty a) nub :: forall a. GHC.Internal.Classes.Eq a => NonEmpty a -> NonEmpty a nubBy :: forall a. (a -> a -> GHC.Internal.Types.Bool) -> NonEmpty a -> NonEmpty a ===================================== testsuite/tests/interface-stability/base-exports.stdout-ws-32 ===================================== @@ -1467,6 +1467,7 @@ module Data.List.NonEmpty where last :: forall a. NonEmpty a -> a length :: forall a. NonEmpty a -> GHC.Internal.Types.Int map :: forall a b. (a -> b) -> NonEmpty a -> NonEmpty b + mapMaybe :: forall a b. (a -> GHC.Internal.Maybe.Maybe b) -> NonEmpty a -> [b] nonEmpty :: forall a. [a] -> GHC.Internal.Maybe.Maybe (NonEmpty a) nub :: forall a. GHC.Internal.Classes.Eq a => NonEmpty a -> NonEmpty a nubBy :: forall a. (a -> a -> GHC.Internal.Types.Bool) -> NonEmpty a -> NonEmpty a View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/cc650b4be2aea55ec0277d1ae8ffd288... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/cc650b4be2aea55ec0277d1ae8ffd288... You're receiving this email because of your account on gitlab.haskell.org.