Expose toHashMapIO from the Data.Fold.Prelude module in "streamly" (#…

…2380)

benchmark/Streamly/Benchmark/Data/Fold.hs

@@ -31,6 +31,7 @@ import Streamly.Internal.Data.IsMap.HashMap ()
 import Streamly.Internal.Data.Array.Mut (MutArray)
 
 import qualified Streamly.Internal.Data.Fold as FL
+import qualified Streamly.Data.Fold.Prelude as Fold
 import qualified Streamly.Internal.Data.Fold.Container as FL
 import qualified Streamly.Internal.Data.Unfold as Unfold
 import qualified Streamly.Internal.Data.Pipe as Pipe
@@ -251,7 +252,7 @@ toIntMapIO f = Stream.fold (FL.toContainerIO f FL.sum)
 {-# INLINE toHashMapIO #-}
 toHashMapIO :: (MonadIO m, Ord k, Num a, Hashable k) =>
     (a -> k) -> Stream m a -> m (HashMap k a)
-toHashMapIO f = Stream.fold (FL.toContainerIO f FL.sum)
+toHashMapIO f = Stream.fold (Fold.toHashMapIO f FL.sum)
 
 -------------------------------------------------------------------------------
 -- unzip

src/Streamly/Data/Fold/Prelude.hs

@@ -0,0 +1,47 @@
+-- |
+-- Module      : Streamly.Data.Fold.Prelude
+-- Copyright   : (c) 2021 Composewell Technologies
+-- License     : BSD-3-Clause
+-- Maintainer  : [email protected]
+-- Stability   : released
+-- Portability : GHC
+--
+module Streamly.Data.Fold.Prelude
+    ( module Streamly.Data.Fold
+    , toHashMapIO
+    )
+where
+
+import Control.Monad.IO.Class (MonadIO)
+import Data.HashMap.Strict (HashMap)
+import Data.Hashable (Hashable)
+import Streamly.Data.Fold
+import Streamly.Internal.Data.Fold.Container (toContainerIO)
+import Streamly.Internal.Data.IsMap.HashMap ()
+
+-- | Split the input stream based on a hashable component of the key field and
+-- fold each split using the given fold. Useful for map/reduce, bucketizing
+-- the input in different bins or for generating histograms.
+--
+-- Example:
+--
+-- >>> import Data.HashMap.Strict (HashMap, fromList)
+-- >>> import qualified Streamly.Data.Fold.Prelude as Fold
+-- >>> import qualified Streamly.Data.Stream as Stream
+-- >>> import Streamly.Data.Fold.Prelude (toHashMapIO)
+-- >>> :{
+--  do
+--  let input = Stream.fromList [("ONE",1),("ONE",1.1),("TWO",2), ("TWO",2.2)]
+--      classify = toHashMapIO fst (Fold.lmap snd Fold.toList)
+--  x <- Stream.fold classify input :: IO (HashMap String [Double])
+--  let y = fromList [("ONE",[1.0,1.1]),("TWO",[2.0,2.2])]
+--  return (x == y)
+-- :}
+-- True
+--
+-- /Pre-release/
+--
+{-# INLINE toHashMapIO #-}
+toHashMapIO :: (MonadIO m, Hashable k, Ord k) =>
+    (a -> k) -> Fold m a b -> Fold m a (HashMap k b)
+toHashMapIO = toContainerIO

streamly.cabal

@@ -353,7 +353,6 @@ library
                      -- Internal modules, listed roughly in bottom up
                      -- dependency order To view dependency graph:
                      -- graphmod | dot -Tps > deps.ps
-
                        Streamly.Internal.Data.IsMap.HashMap
                      , Streamly.Internal.Data.Cont
                      , Streamly.Internal.Data.Stream.MkType
@@ -396,6 +395,7 @@ library
                      -- Exposed modules
                      , Streamly.Data.Stream.MkType
                      , Streamly.Data.Stream.Prelude
+                     , Streamly.Data.Fold.Prelude
 
                      -- Network/IO
                      , Streamly.Network.Socket