Move Statistics data type to a separate submodule of Utils

To avoid further cluttering the already overly long Utils.hs
move the Statistics data type with its related functions into
a separate submodule. This also provides a better encapsulation
of this type where the Constructors are not exported.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

Makefile.am

@@ -157,7 +157,8 @@ HS_DIRS = \
 	test/hs/Test/Ganeti/Hypervisor/Xen \
 	test/hs/Test/Ganeti/Locking \
 	test/hs/Test/Ganeti/Query \
-	test/hs/Test/Ganeti/THH
+	test/hs/Test/Ganeti/THH \
+	test/hs/Test/Ganeti/Utils
 
 # Haskell directories without the roots (src, test/hs)
 HS_DIRS_NOROOT = $(filter-out src,$(filter-out test/hs,$(HS_DIRS)))
@@ -865,6 +866,7 @@ HS_LIB_SRCS = \
 	src/Ganeti/Utils/MonadPlus.hs \
 	src/Ganeti/Utils/MultiMap.hs \
 	src/Ganeti/Utils/MVarLock.hs \
+	src/Ganeti/Utils/Statistics.hs \
 	src/Ganeti/VCluster.hs \
 	src/Ganeti/WConfd/ConfigState.hs \
 	src/Ganeti/WConfd/ConfigWriter.hs \
@@ -930,7 +932,9 @@ HS_TEST_SRCS = \
 	test/hs/Test/Ganeti/TestHTools.hs \
 	test/hs/Test/Ganeti/TestHelper.hs \
 	test/hs/Test/Ganeti/Types.hs \
-	test/hs/Test/Ganeti/Utils.hs
+	test/hs/Test/Ganeti/Utils.hs \
+	test/hs/Test/Ganeti/Utils/Statistics.hs
+
 
 HS_LIBTEST_SRCS = $(HS_LIB_SRCS) $(HS_TEST_SRCS)
 

src/Ganeti/HTools/Cluster.hs

@@ -95,6 +95,7 @@ import Ganeti.HTools.Types
 import Ganeti.Compat
 import qualified Ganeti.OpCodes as OpCodes
 import Ganeti.Utils
+import Ganeti.Utils.Statistics
 import Ganeti.Types (EvacMode(..), mkNonEmpty)
 
 -- * Types

src/Ganeti/Utils.hs

-{-# LANGUAGE FlexibleContexts, BangPatterns #-}
+{-# LANGUAGE FlexibleContexts #-}
 
 {-| Utility functions. -}
 
@@ -29,11 +29,6 @@ module Ganeti.Utils
   , debugXy
   , sepSplit
   , findFirst
-  , Statistics
-  , getSumStatistics
-  , getStdDevStatistics
-  , getStatisticValue
-  , updateStatistics
   , stdDev
   , if'
   , select
@@ -194,48 +189,6 @@ stdDev lst =
       av = foldl' (\accu em -> let d = em - mv in accu + d * d) 0.0 lst
   in sqrt (av / ll) -- stddev
 
--- | Abstract type of statistical accumulations. They behave as if the given
--- statistics were computed on the list of values, but they allow a potentially
--- more efficient update of a given value.
-data Statistics = SumStatistics Double
-                | StdDevStatistics Double Double Double deriving Show
-                  -- count, sum, and not the sum of squares---instead the
-                  -- computed variance for better precission.
-
--- | Get a statistics that sums up the values.
-getSumStatistics :: [Double] -> Statistics
-getSumStatistics = SumStatistics . sum
-
--- | Get a statistics for the standard deviation.
-getStdDevStatistics :: [Double] -> Statistics
-getStdDevStatistics xs =
-  let (nt, st) = foldl' (\(n, s) x ->
-                            let !n' = n + 1
-                                !s' = s + x
-                            in (n', s'))
-                 (0, 0) xs
-      mean = st / nt
-      nvar = foldl' (\v x -> let d = x - mean in v + d * d) 0 xs
-  in StdDevStatistics nt st (nvar / nt)
-
--- | Obtain the value of a statistics.
-getStatisticValue :: Statistics -> Double
-getStatisticValue (SumStatistics s) = s
-getStatisticValue (StdDevStatistics _ _ var) = sqrt var
-
--- | In a given statistics replace on value by another. This
--- will only give meaningful results, if the original value
--- was actually part of the statistics.
-updateStatistics :: Statistics -> (Double, Double) -> Statistics
-updateStatistics (SumStatistics s) (x, y) = SumStatistics $ s +  (y - x)
-updateStatistics (StdDevStatistics n s var) (x, y) =
-  let !ds = y - x
-      !dss = y * y - x * x
-      !dnnvar = n * dss - (2 * s + ds) * ds
-      !s' = s + ds
-      !var' = max 0 $ var + dnnvar / (n * n)
-  in StdDevStatistics n s' var'
-
 -- *  Logical functions
 
 -- Avoid syntactic sugar and enhance readability. These functions are proposed

src/Ganeti/Utils/Statistics.hs

+{-# LANGUAGE BangPatterns #-}
+
+
+{-| Utility functions for statistical accumulation. -}
+
+{-
+
+Copyright (C) 2014 Google Inc.
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA.
+
+-}
+
+module Ganeti.Utils.Statistics
+  ( Statistics
+  , getSumStatistics
+  , getStdDevStatistics
+  , getStatisticValue
+  , updateStatistics
+  ) where
+
+import Data.List (foldl')
+
+-- | Abstract type of statistical accumulations. They behave as if the given
+-- statistics were computed on the list of values, but they allow a potentially
+-- more efficient update of a given value.
+data Statistics = SumStatistics Double
+                | StdDevStatistics Double Double Double deriving Show
+                  -- count, sum, and not the sum of squares---instead the
+                  -- computed variance for better precission.
+
+-- | Get a statistics that sums up the values.
+getSumStatistics :: [Double] -> Statistics
+getSumStatistics = SumStatistics . sum
+
+-- | Get a statistics for the standard deviation.
+getStdDevStatistics :: [Double] -> Statistics
+getStdDevStatistics xs =
+  let (nt, st) = foldl' (\(n, s) x ->
+                            let !n' = n + 1
+                                !s' = s + x
+                            in (n', s'))
+                 (0, 0) xs
+      mean = st / nt
+      nvar = foldl' (\v x -> let d = x - mean in v + d * d) 0 xs
+  in StdDevStatistics nt st (nvar / nt)
+
+-- | Obtain the value of a statistics.
+getStatisticValue :: Statistics -> Double
+getStatisticValue (SumStatistics s) = s
+getStatisticValue (StdDevStatistics _ _ var) = sqrt var
+
+-- | In a given statistics replace on value by another. This
+-- will only give meaningful results, if the original value
+-- was actually part of the statistics.
+updateStatistics :: Statistics -> (Double, Double) -> Statistics
+updateStatistics (SumStatistics s) (x, y) = SumStatistics $ s +  (y - x)
+updateStatistics (StdDevStatistics n s var) (x, y) =
+  let !ds = y - x
+      !dss = y * y - x * x
+      !dnnvar = n * dss - (2 * s + ds) * ds
+      !s' = s + ds
+      !var' = max 0 $ var + dnnvar / (n * n)
+  in StdDevStatistics n s' var'
+

test/hs/Test/Ganeti/Utils.hs

@@ -341,24 +341,6 @@ prop_splitRecombineEithers es =
         (splitleft, splitright, trail) = splitEithers es
         emptylist = []::[Int]
 
--- | Test the update function for standard deviations against the naive
--- implementation.
-prop_stddev_update :: Property
-prop_stddev_update =
-  forAll (choose (0, 6) >>= flip vectorOf (choose (0, 1))) $ \xs ->
-  forAll (choose (0, 1)) $ \a ->
-  forAll (choose (0, 1)) $ \b ->
-  forAll (choose (1, 6) >>= flip vectorOf (choose (0, 1))) $ \ys ->
-  let original = xs ++ [a] ++ ys
-      modified = xs ++ [b] ++ ys
-      with_update = getStatisticValue
-                    $ updateStatistics (getStdDevStatistics original) (a,b)
-      direct = stdDev modified
-  in printTestCase ("Value computed by update " ++ show with_update
-                    ++ " differs too much from correct value " ++ show direct)
-                   (abs (with_update - direct) < 1e-12)
-
--- | Test list for the Utils module.
 testSuite "Utils"
             [ 'prop_commaJoinSplit
             , 'prop_commaSplitJoin
@@ -385,5 +367,4 @@ testSuite "Utils"
             , 'prop_chompPrefix_empty_string
             , 'prop_chompPrefix_nothing
             , 'prop_splitRecombineEithers
-            , 'prop_stddev_update
             ]

test/hs/Test/Ganeti/Utils/Statistics.hs

+{-# LANGUAGE TemplateHaskell #-}
+
+{-| Unit tests for Ganeti statistics utils.
+
+-}
+
+{-
+
+Copyright (C) 2014 Google Inc.
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA.
+
+-}
+
+module Test.Ganeti.Utils.Statistics (testUtils_Statistics) where
+
+import Test.QuickCheck
+
+import Test.Ganeti.TestHelper
+
+import Ganeti.Utils (stdDev)
+import Ganeti.Utils.Statistics
+
+-- | Test the update function for standard deviations against the naive
+-- implementation.
+prop_stddev_update :: Property
+prop_stddev_update =
+  forAll (choose (0, 6) >>= flip vectorOf (choose (0, 1))) $ \xs ->
+  forAll (choose (0, 1)) $ \a ->
+  forAll (choose (0, 1)) $ \b ->
+  forAll (choose (1, 6) >>= flip vectorOf (choose (0, 1))) $ \ys ->
+  let original = xs ++ [a] ++ ys
+      modified = xs ++ [b] ++ ys
+      with_update = getStatisticValue
+                    $ updateStatistics (getStdDevStatistics original) (a,b)
+      direct = stdDev modified
+  in printTestCase ("Value computed by update " ++ show with_update
+                    ++ " differs too much from correct value " ++ show direct)
+                   (abs (with_update - direct) < 1e-12)
+
+testSuite "Utils/Statistics"
+  [ 'prop_stddev_update
+  ]

test/hs/htest.hs

@@ -80,6 +80,7 @@ import Test.Ganeti.THH
 import Test.Ganeti.THH.Types
 import Test.Ganeti.Types
 import Test.Ganeti.Utils
+import Test.Ganeti.Utils.Statistics
 
 -- | Our default test options, overring the built-in test-framework
 -- ones (but not the supplied command line parameters).
@@ -145,6 +146,7 @@ allTests =
   , testTHH_Types
   , testTypes
   , testUtils
+  , testUtils_Statistics
   ]
 
 -- | Main function. Note we don't use defaultMain since we want to