+{-# LANGUAGE BangPatterns #-}
+
-- | The Misc module contains helper functions that seem out of place
-- anywhere else.
-module Misc
+--
+module Misc (
+ all_equal,
+ disjoint,
+ factorial,
+ flatten,
+ misc_properties,
+ misc_tests,
+ transpose_xz )
where
+import qualified Data.Vector as V ( Vector, elem, empty, filter )
+import Test.Tasty ( TestTree, testGroup )
+import Test.Tasty.HUnit ( Assertion, assertEqual, testCase )
+import Test.Tasty.QuickCheck ( Property, (==>), testProperty )
+
-- | The standard factorial function. See
-- <http://www.willamette.edu/~fruehr/haskell/evolution.html> for
-- possible improvements.
+--
+-- Examples:
+--
+-- >>> factorial 0
+-- 1
+--
+-- >>> factorial 4
+-- 24
+--
factorial :: Int -> Int
-factorial n
- | n <= 1 = 1
- | n > 20 = error "integer overflow in factorial function"
- | otherwise = product [1..n]
-
+factorial !n =
+ go 1 n
+ where
+ go :: Int -> Int -> Int
+ 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.
+--
+-- Examples:
+--
+-- >>> flatten [ [[1,2], [3,4]], [[5,6], [7,8]] ]
+-- [1,2,3,4,5,6,7,8]
+--
flatten :: [[[a]]] -> [a]
flatten xs = concat $ concat xs
+
+
+-- | Switch the x and z dimensions of a three-dimensional list.
+transpose_xz :: [[[a]]] -> [[[a]]]
+transpose_xz [] = []
+transpose_xz [[]] = [[]]
+transpose_xz [[[]]] = [[[]]]
+transpose_xz m =
+ [[[ m !! x !! y !! z | x <- [0..xsize]]
+ | y <- [0..ysize]]
+ | z <- [0..zsize]]
+ where
+ zsize = (length m) - 1
+ ysize = length (head m) - 1
+ xsize = length (head $ head m) - 1
+
+-- | Takes a list, and returns True if its elements are pairwise
+-- equal. Returns False otherwise.
+--
+-- Only used in tests.
+--
+all_equal :: (Eq a) => [a] -> Bool
+all_equal [] = True -- Vacuously
+all_equal (x:xs) = all (== x) xs
+
+
+
+-- | Returns 'True' if the vectors xs and ys are disjoint, 'False'
+-- otherwise.
+--
+-- Examples:
+--
+-- >>> let xs = Data.Vector.fromList [1,2,3]
+-- >>> let ys = Data.Vector.fromList [4,5,6]
+-- >>> disjoint xs ys
+-- True
+--
+-- >>> let ys = Data.Vector.fromList [3,4,5]
+-- >>> disjoint xs ys
+-- False
+--
+-- Only used in tests.
+--
+disjoint :: (Eq a) => V.Vector a -> V.Vector a -> Bool
+disjoint 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 =
+ n <= 20 ==> factorial n >= n
+
+
+test_flatten1 :: Assertion
+test_flatten1 =
+ assertEqual "flatten actually works" expected_list actual_list
+ where
+ target = [[[1::Int]], [[2, 3]]]
+ expected_list = [1, 2, 3] :: [Int]
+ actual_list = flatten target
+
+
+misc_tests :: TestTree
+misc_tests =
+ testGroup "Misc tests" [
+ testCase "flatten (1)" test_flatten1 ]
+
+
+misc_properties :: TestTree
+misc_properties =
+ testGroup "Misc properties" [
+ testProperty "factorial greater" prop_factorial_greater ]