src/Misc.hs

   1 {-# LANGUAGE BangPatterns #-}
   2 -- | The Misc module contains helper functions that seem out of place
   3 --   anywhere else.
   4 module Misc
   5 where
   6
   7 import qualified Data.Vector as V (Vector, elem, empty, filter)
   8 import Test.Framework (Test, testGroup)
   9 import Test.Framework.Providers.HUnit (testCase)
  10 import Test.Framework.Providers.QuickCheck2 (testProperty)
  11 import Test.HUnit (Assertion, assertEqual)
  12 import Test.QuickCheck
  13
  14
  15 -- | The standard factorial function. See
  16 --   <http://www.willamette.edu/~fruehr/haskell/evolution.html> for
  17 --   possible improvements.
  18 --
  19 --   Examples:
  20 --
  21 --   >>> factorial 0
  22 --   1
  23 --
  24 --   >>> factorial 4
  25 --   24
  26 --
  27 factorial :: Int -> Int
  28 factorial !n
  29     | n > 20    = error "integer overflow in factorial function"
  30     | otherwise = go 1 n
  31     where go !acc !i
  32                 | i <= 1    = acc
  33                 | otherwise = go (acc * i) (i - 1)
  34
  35 -- | Takes a three-dimensional list, and flattens it into a
  36 --   one-dimensional one.
  37 --
  38 --  Examples:
  39 --
  40 --  >>> flatten [ [[1,2], [3,4]], [[5,6], [7,8]] ]
  41 --  [1,2,3,4,5,6,7,8]
  42 --
  43 flatten :: [[[a]]] -> [a]
  44 flatten xs = concat $ concat xs
  45
  46
  47 -- | Switch the x and z dimensions of a three-dimensional list.
  48 transpose_xz :: [[[a]]] -> [[[a]]]
  49 transpose_xz [] = []
  50 transpose_xz [[]] = [[]]
  51 transpose_xz [[[]]] = [[[]]]
  52 transpose_xz m =
  53     [[[ m !! x !! y !! z | x <- [0..xsize]]
  54                       | y <- [0..ysize]]
  55                       | z <- [0..zsize]]
  56     where
  57       zsize = (length m) - 1
  58       ysize = length (head m) - 1
  59       xsize = length (head $ head m) - 1
  60
  61 -- | Takes a list, and returns True if its elements are pairwise
  62 --   equal. Returns False otherwise.
  63 --
  64 --   Only used in tests.
  65 --
  66 all_equal :: (Eq a) => [a] -> Bool
  67 all_equal xs =
  68     all (== first_element) other_elements
  69     where
  70       first_element  = head xs
  71       other_elements = tail xs
  72
  73
  74 -- | Returns 'True' if the vectors xs and ys are disjoint, 'False'
  75 --   otherwise.
  76 --
  77 --   Examples:
  78 --
  79 --   >>> let xs = Data.Vector.fromList [1,2,3]
  80 --   >>> let ys = Data.Vector.fromList [4,5,6]
  81 --   >>> disjoint xs ys
  82 --   True
  83 --
  84 --   >>> let ys = Data.Vector.fromList [3,4,5]
  85 --   >>> disjoint xs ys
  86 --   False
  87 --
  88 --   Only used in tests.
  89 --
  90 disjoint :: (Eq a) => V.Vector a -> V.Vector a -> Bool
  91 disjoint xs ys =
  92   intersect xs ys == V.empty
  93   where
  94     intersect :: (Eq a) => V.Vector a -> V.Vector a -> V.Vector a
  95     intersect ws zs =
  96       V.filter (`V.elem` zs) ws
  97
  98 prop_factorial_greater :: Int -> Property
  99 prop_factorial_greater n =
 100     n <= 20 ==> factorial n >= n
 101
 102
 103 test_flatten1 :: Assertion
 104 test_flatten1 =
 105     assertEqual "flatten actually works" expected_list actual_list
 106     where
 107       target = [[[1::Int]], [[2, 3]]]
 108       expected_list = [1, 2, 3]
 109       actual_list = flatten target
 110
 111
 112 misc_tests :: Test.Framework.Test
 113 misc_tests =
 114     testGroup "Misc Tests" [
 115       testCase "flatten (1)" test_flatten1 ]
 116
 117
 118 misc_properties :: Test.Framework.Test
 119 misc_properties =
 120     testGroup "Misc Properties" [
 121       testProperty "factorial greater" prop_factorial_greater ]