Add bang patterns to the Misc module and use them to write a faster

[spline3.git] / src / Misc.hs

diff --git a/src/Misc.hs b/src/Misc.hs
index 16b0ead151ad1b29190028db01aa98ef34d6b797..4b285e4cc3b0cff1f8344aa09c905ed6b0c3fe99 100644 (file)
--- a/src/Misc.hs
+++ b/src/Misc.hs
@@ -1,13 +1,14 @@
+{-# LANGUAGE BangPatterns #-}
 -- | The Misc module contains helper functions that seem out of place
 --   anywhere else.
 module Misc
 where
 
-import Data.List (intersect)
+import qualified Data.Vector as V (Vector, elem, empty, filter)
 import Test.Framework (Test, testGroup)
 import Test.Framework.Providers.HUnit (testCase)
 import Test.Framework.Providers.QuickCheck2 (testProperty)
-import Test.HUnit
+import Test.HUnit (Assertion, assertEqual)
 import Test.QuickCheck
 
 
@@ -24,11 +25,12 @@ import Test.QuickCheck
 --   24
 --
 factorial :: Int -> Int
-factorial n
-    | n <= 1 = 1
-    | n > 20 = error "integer overflow in factorial function"
-    | otherwise = product [1..n]
-
+factorial !n
+    | n > 20    = error "integer overflow in factorial function"
+    | otherwise = go 1 n
+    where go !acc !i
+                | i <= 1    = acc
+                | otherwise = go (acc * i) (i - 1)
 
 -- | Takes a three-dimensional list, and flattens it into a
 --   one-dimensional one.
@@ -66,22 +68,27 @@ all_equal xs =
       other_elements = tail xs
 
 
--- | Returns 'True' if the lists xs and ys are disjoint, 'False'
+-- | Returns 'True' if the vectors xs and ys are disjoint, 'False'
 --   otherwise.
 --
 --   Examples:
 --
---   >>> disjoint [1,2,3] [4,5,6]
+--   >>> let xs = Data.Vector.fromList [1,2,3]
+--   >>> let ys = Data.Vector.fromList [4,5,6]
+--   >>> disjoint xs ys
 --   True
 --
---   >>>  disjoint [1,2,3] [3,4,5]
+--   >>> let ys = Data.Vector.fromList [3,4,5]
+--   >>> disjoint xs ys
 --   False
 --
-disjoint :: (Eq a) => [a] -> [a] -> Bool
+disjoint :: (Eq a) => V.Vector a -> V.Vector a -> Bool
 disjoint xs ys =
-    intersect xs ys == []
-
-
+  intersect xs ys == V.empty
+  where
+    intersect :: (Eq a) => V.Vector a -> V.Vector a -> V.Vector a
+    intersect ws zs =
+      V.filter (`V.elem` zs) ws
 
 prop_factorial_greater :: Int -> Property
 prop_factorial_greater n =