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 all_equal :: (Eq a) => [a] -> Bool
  64 all_equal xs =
  65     all (== first_element) other_elements
  66     where
  67       first_element  = head xs
  68       other_elements = tail xs
  69
  70
  71 -- | Returns 'True' if the vectors xs and ys are disjoint, 'False'
  72 --   otherwise.
  73 --
  74 --   Examples:
  75 --
  76 --   >>> let xs = Data.Vector.fromList [1,2,3]
  77 --   >>> let ys = Data.Vector.fromList [4,5,6]
  78 --   >>> disjoint xs ys
  79 --   True
  80 --
  81 --   >>> let ys = Data.Vector.fromList [3,4,5]
  82 --   >>> disjoint xs ys
  83 --   False
  84 --
  85 disjoint :: (Eq a) => V.Vector a -> V.Vector a -> Bool
  86 disjoint xs ys =
  87   intersect xs ys == V.empty
  88   where
  89     intersect :: (Eq a) => V.Vector a -> V.Vector a -> V.Vector a
  90     intersect ws zs =
  91       V.filter (`V.elem` zs) ws
  92
  93 prop_factorial_greater :: Int -> Property
  94 prop_factorial_greater n =
  95     n <= 20 ==> factorial n >= n
  96
  97
  98 test_flatten1 :: Assertion
  99 test_flatten1 =
 100     assertEqual "flatten actually works" expected_list actual_list
 101     where
 102       target = [[[1::Int]], [[2, 3]]]
 103       expected_list = [1, 2, 3]
 104       actual_list = flatten target
 105
 106
 107 misc_tests :: Test.Framework.Test
 108 misc_tests =
 109     testGroup "Misc Tests" [
 110       testCase "flatten (1)" test_flatten1 ]
 111
 112
 113 misc_properties :: Test.Framework.Test
 114 misc_properties =
 115     testGroup "Misc Properties" [
 116       testProperty "factorial greater" prop_factorial_greater ]