mighty-metropolis

commit 0818743b94bd958646d48cd1fdbd0dd87f4e8135
parent 8c9d07f20deaaf98ddf5c9b834bf82d2f57a9680
Author: Jared Tobin <jared@jtobin.io>
Date:   Thu, 21 May 2020 20:59:50 +0400

Pull in foldl dependency for tests.

Diffstat:
M
mighty-metropolis.cabal
 | 
1
+
M
test/Spec.hs
 | 
11
++++++-----

2 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/mighty-metropolis.cabal b/mighty-metropolis.cabal
@@ -81,6 +81,7 @@ Test-suite tests
   build-depends:
       base              >= 4 && < 6
     , containers        >= 0.5 && < 0.7
+    , foldl
     , mighty-metropolis
     , mwc-probability   >= 1.0.1
     , hspec
diff --git a/test/Spec.hs b/test/Spec.hs
@@ -1,6 +1,7 @@
 {-# OPTIONS_GHC -Wall #-}
 {-# LANGUAGE RecordWildCards #-}
 
+import qualified Control.Foldl as L
 import Data.Functor.Identity
 import Data.Maybe (mapMaybe)
 import Data.Sampling.Types
@@ -16,13 +17,13 @@ withinPercent b n a
     d = abs (a - b)
 
 mean :: [Double] -> Double
-mean xs = sum xs / n where
-  n = fromIntegral (length xs)
+mean = L.fold L.mean
 
 variance :: [Double] -> Double
-variance xs = sum [(x - m) ** 2.0 | x <- xs] / (n - 1) where
-  m = mean xs
-  n = fromIntegral (length xs)
+variance xs = L.fold alg xs where
+  alg = (/) <$> L.premap csq L.sum <*> L.genericLength - 1
+  csq = (** 2.0) . subtract m
+  m   = mean xs
 
 stdDev :: [Double] -> Double
 stdDev = sqrt . variance