src/Misc.hs

   1 -- | The Misc module contains helper functions that seem out of place
   2 --   anywhere else.
   3 module Misc
   4 where
   5
   6 import Data.List (intersect)
   7
   8
   9 -- | The standard factorial function. See
  10 --   <http://www.willamette.edu/~fruehr/haskell/evolution.html> for
  11 --   possible improvements.
  12 --
  13 --   Examples:
  14 --
  15 --   >>> factorial 0
  16 --   1
  17 --
  18 --   >>> factorial 4
  19 --   24
  20 --
  21 factorial :: Int -> Int
  22 factorial n
  23     | n <= 1 = 1
  24     | n > 20 = error "integer overflow in factorial function"
  25     | otherwise = product [1..n]
  26
  27
  28 -- | Takes a three-dimensional list, and flattens it into a
  29 --   one-dimensional one.
  30 --
  31 --  Examples:
  32 --
  33 --  >>> flatten [ [[1,2], [3,4]], [[5,6], [7,8]] ]
  34 --  [1,2,3,4,5,6,7,8]
  35 --
  36 flatten :: [[[a]]] -> [a]
  37 flatten xs = concat $ concat xs
  38
  39
  40 -- | Switch the x and z dimensions of a three-dimensional list.
  41 transpose_xz :: [[[a]]] -> [[[a]]]
  42 transpose_xz [] = []
  43 transpose_xz [[]] = [[]]
  44 transpose_xz [[[]]] = [[[]]]
  45 transpose_xz m =
  46     [[[ m !! x !! y !! z | x <- [0..xsize]]
  47                       | y <- [0..ysize]]
  48                       | z <- [0..zsize]]
  49     where
  50       zsize = (length m) - 1
  51       ysize = length (head m) - 1
  52       xsize = length (head $ head m) - 1
  53
  54 -- | Takes a list, and returns True if its elements are pairwise
  55 --   equal. Returns False otherwise.
  56 all_equal :: (Eq a) => [a] -> Bool
  57 all_equal xs =
  58     all (== first_element) other_elements
  59     where
  60       first_element  = head xs
  61       other_elements = tail xs
  62
  63
  64 -- | Returns 'True' if the lists xs and ys are disjoint, 'False'
  65 --   otherwise.
  66 --
  67 --   Examples:
  68 --
  69 --   >>> disjoint [1,2,3] [4,5,6]
  70 --   True
  71 --
  72 --   >>>  disjoint [1,2,3] [3,4,5]
  73 --   False
  74 --
  75 disjoint :: (Eq a) => [a] -> [a] -> Bool
  76 disjoint xs ys =
  77     intersect xs ys == []