Merge pull request serokell#257 from serokell/dk318/serokell#199-conc…

…atMap-type-changing

[serokell#199] `concatMap` type change

CHANGES.md

@@ -19,6 +19,10 @@ Unreleased
   Change the type of `readMaybe` from `readMaybe :: Read a => String -> Maybe a`
   to it's polymorphic version `readMaybe :: forall b a. (ToString a, Read b) => a -> Maybe b`.
 
+* [#199](https://github.com/serokell/universum/issues/199):
+  Change type of `concatMap` from `concatMap :: Foldable f => (a -> [b]) -> t a -> [b]`
+  to `concatMap :: Container c => (Element c -> [b]) -> c -> [b]`.
+
 1.7.3
 =====
 

src/Universum/Base.hs

@@ -58,7 +58,7 @@ import System.IO (FilePath, Handle, IOMode (..), stderr, stdin, stdout)
 
 -- Base typeclasses
 import Data.Eq (Eq (..))
-import Data.Foldable (Foldable, concat, concatMap, foldlM, foldrM)
+import Data.Foldable (Foldable, concat, foldlM, foldrM)
 import Data.Kind (Constraint, Type)
 import Data.Ord (Down (..), Ord (..), Ordering (..), comparing)
 import Data.Traversable (Traversable (..), fmapDefault, foldMapDefault, forM, mapAccumL, mapAccumR)

src/Universum/Container/Class.hs

@@ -39,14 +39,15 @@ module Universum.Container.Class
        , sequenceA_
        , sequence_
        , asum
+       , concatMap
 
          -- * Others
        , One(..)
        ) where
 
 import Data.Coerce (Coercible, coerce)
 import Data.Kind (Type)
-import Prelude hiding (all, and, any, elem, foldMap, foldl, foldr, mapM_, notElem, null, or, print,
+import Prelude hiding (all, and, any, concatMap, elem, foldMap, foldl, foldr, mapM_, notElem, null, or, print,
                 product, sequence_, sum)
 
 import Universum.Applicative (Alternative (..), Const, ZipList (..), pass)
@@ -69,6 +70,8 @@ import qualified Data.Sequence as SEQ
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Lazy as BSL
 
+import qualified Data.List (concatMap)
+
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL
 
@@ -746,6 +749,16 @@ asum
 asum = foldr (<|>) empty
 {-# INLINE asum #-}
 
+{- | Version of 'Data.Foldable.concatMap' constrained to 'Container'.
+
+>>> concatMap (\x -> [x + 1, x + 2]) [1, 2, 3]
+[2,3,3,4,4,5]
+
+-}
+concatMap :: Container c => (Element c -> [b]) -> c -> [b]
+concatMap f = Data.List.concatMap f . toList
+{-# INLINE concatMap #-}
+
 ----------------------------------------------------------------------------
 -- Disallowed instances
 ----------------------------------------------------------------------------