Rename Count, it's not really a count

src/Warden/Data/Numeric.hs

@@ -6,7 +6,7 @@
 {-# LANGUAGE DeriveGeneric #-}
 
 module Warden.Data.Numeric (
-    Count(..)
+    KAcc(..)
   , Maximum(..)
   , Mean(..)
   , MeanAcc(..)
@@ -71,12 +71,14 @@ instance Monoid Maximum where
           else Maximum prev
   {-# INLINE mappend #-}
 
-newtype Count =
-  Count {
-    getCount :: Int
+-- | Counter param for mean/stddev calculation. Equal to one plus the number
+-- of records seen.
+newtype KAcc =
+  KAcc {
+    getKAcc :: Int
   } deriving (Eq, Show, ToJSON, FromJSON, Generic, Num)
 
-instance NFData Count
+instance NFData KAcc
 
 -- | Preliminary mean, still accumulating.
 newtype MeanAcc =
@@ -101,8 +103,10 @@ data Median =
 
 instance NFData Median
 
-newtype StdDevAcc = StdDevAcc { unStdDevAcc :: Double }
-  deriving (Eq, Show, ToJSON, FromJSON, Generic)
+newtype StdDevAcc =
+  StdDevAcc {
+    unStdDevAcc :: Double
+  } deriving (Eq, Show, ToJSON, FromJSON, Generic)
 
 instance NFData StdDevAcc
 
@@ -138,7 +142,7 @@ instance NFData NumericSummary
 
 data MeanDevAcc =
     MeanDevInitial
-  | MeanDevAcc {-# UNPACK #-} !MeanAcc !(Maybe StdDevAcc) {-# UNPACK #-} !Count
+  | MeanDevAcc {-# UNPACK #-} !MeanAcc !(Maybe StdDevAcc) {-# UNPACK #-} !KAcc
   deriving (Eq, Show, Generic)
 
 instance NFData MeanDevAcc

src/Warden/Numeric.hs

@@ -1,4 +1,4 @@
- {-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE BangPatterns #-}
 
 module Warden.Numeric (
@@ -46,17 +46,17 @@ updateMeanDev :: Real a
 updateMeanDev !macc x =
   let x' = (fromRational . toRational) x in case macc of
   MeanDevInitial ->
-    let i = Count 1
+    let i = KAcc 1
         m = MeanAcc 0
         s = Nothing
     in update' m s i x'
   (MeanDevAcc m s i) ->
     update' m s i x'
   where
-    update' (MeanAcc m) s (Count i) v =
+    update' (MeanAcc m) s (KAcc i) v =
       let delta = v - m
           m'    = MeanAcc $ m + delta / (fromIntegral i)
-          i'    = Count $ i + 1
+          i'    = KAcc $ i + 1
           s'    = case s of
                     Nothing ->
                       Just $ StdDevAcc 0
@@ -100,7 +100,7 @@ combineMeanDevAcc (MeanDevAcc mu1 s1 c1) (MeanDevAcc mu2 s2 c2) =
       sda' = combineStdDevAcc mu' (mu1, s1, c1) (mu2, s2, c2)
       -- KAccs are off-by-one from the actual number of values seen, so
       -- subtract one from the sum to prevent it becoming off-by-two.
-      c' = c1 + c2 - (Count 1) in
+      c' = c1 + c2 - (KAcc 1) in
   MeanDevAcc mu' sda' c'
 {-# INLINE combineMeanDevAcc #-}
 
@@ -144,8 +144,8 @@ combineVariance (MeanAcc muHat) (MeanAcc mu1, Variance var1, KAcc c1) (MeanAcc m
 {-# INLINE combineVariance #-}
 
 -- | Combine mean of two subsets, given subset means and size.
-combineMeanAcc :: (MeanAcc, Count) -> (MeanAcc, Count) -> MeanAcc
-combineMeanAcc (MeanAcc mu1, Count c1) (MeanAcc mu2, Count c2) =
+combineMeanAcc :: (MeanAcc, KAcc) -> (MeanAcc, KAcc) -> MeanAcc
+combineMeanAcc (MeanAcc mu1, KAcc c1) (MeanAcc mu2, KAcc c2) =
   let c1' = fromIntegral c1
       c2' = fromIntegral c2 in
   MeanAcc $ ((mu1 * c1') + (mu2 * c2')) / (c1' + c2')

test/Test/Warden/Numeric.hs

@@ -89,10 +89,10 @@ prop_updateMeanDev (NPlus n) = forAll (vectorOf n (arbitrary :: Gen Double)) $ \
       var = textbookVariance mu xs
       sd = StdDev $ sqrt var
       uMeanDev = (Mean mu, sd) in
-  (nsMeanDev, Just (n+1)) ~~~ (uMeanDev, meanDevCount mda)
+  (nsMeanDev, Just (n+1)) ~~~ (uMeanDev, meanDevKAcc mda)
   where
-    meanDevCount MeanDevInitial = Nothing
-    meanDevCount (MeanDevAcc _ _ (Count c)) = Just c
+    meanDevKAcc MeanDevInitial = Nothing
+    meanDevKAcc (MeanDevAcc _ _ (KAcc c)) = Just c
 
 prop_updateMeanDev_associative :: Int -> Property
 prop_updateMeanDev_associative n = forAll (vectorOf n (arbitrary :: Gen Double)) $ \xs ->