Deprecate variance and stdDev in folds

benchmark/Streamly/Benchmark/Data/Fold.hs

@@ -8,6 +8,7 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
 
 module Main (main) where
 

core/src/Streamly/Data/Fold.hs

@@ -162,8 +162,6 @@ module Streamly.Data.Fold
     , minimumBy
     , minimum
     , mean
-    , variance
-    , stdDev
     , rollingHash
     , rollingHashWithSalt
 
@@ -270,6 +268,8 @@ module Streamly.Data.Fold
     -- * Deprecated
     , sequence
     , mapM
+    , variance
+    , stdDev
     )
 where
 

core/src/Streamly/Internal/Data/Fold.hs

@@ -57,8 +57,6 @@ module Streamly.Internal.Data.Fold
     , countDistinct
     , countDistinctInt
     , mean
-    , variance
-    , stdDev
     , rollingHash
     , rollingHashWithSalt
     , rollingHashFirstN
@@ -285,6 +283,8 @@ module Streamly.Internal.Data.Fold
     -- * Deprecated
     , sequence
     , mapM
+    , variance
+    , stdDev
     )
 where
 
@@ -794,6 +794,7 @@ mean = fmap done $ foldl' step begin
 -- the input stream.
 --
 -- @since 0.7.0
+{-# DEPRECATED variance "Use the streamly-statistics package instead" #-}
 {-# INLINE variance #-}
 variance :: (Monad m, Fractional a) => Fold m a a
 variance = fmap done $ foldl' step begin
@@ -817,6 +818,7 @@ variance = fmap done $ foldl' step begin
 -- elements in the input stream.
 --
 -- @since 0.7.0
+{-# DEPRECATED stdDev "Use the streamly-statistics package instead" #-}
 {-# INLINE stdDev #-}
 stdDev :: (Monad m, Floating a) => Fold m a a
 stdDev = sqrt <$> variance

docs/User/ProjectRelated/Changelog.md

@@ -8,6 +8,13 @@
     readChunksWithBufferOf -> readChunksWith
     writeWithBufferOf -> writeWith
     writeChunksWithBufferOf -> writeChunksWith
+
+### Deprecations
+
+* In `Streamly.Data.Fold`:
+  * `variance`, and `stdDev` have been deprecated. Please use the
+    `streamly-statistics` package instead.
+
 ## 0.8.2 (Mar 2022)
 
 * Fix performance issues for GHC-9. These changes coupled with GHC changes

test/Streamly/Test/Data/Fold.hs

@@ -1,3 +1,5 @@
+{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
+
 module Main (main) where
 
 import Data.List (sort)