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
   7 -- | The standard factorial function. See
   8 --   <http://www.willamette.edu/~fruehr/haskell/evolution.html> for
   9 --   possible improvements.
  10 --
  11 --   Examples:
  12 --
  13 --   >>> factorial 0
  14 --   1
  15 --
  16 --   >>> factorial 4
  17 --   24
  18 --
  19 factorial :: Int -> Int
  20 factorial n
  21     | n <= 1 = 1
  22     | n > 20 = error "integer overflow in factorial function"
  23     | otherwise = product [1..n]
  24
  25
  26 -- | Takes a three-dimensional list, and flattens it into a
  27 --   one-dimensional one.
  28 --
  29 --  Examples:
  30 --
  31 --  >>> flatten [ [[1,2], [3,4]], [[5,6], [7,8]] ]
  32 --  [1,2,3,4,5,6,7,8]
  33 --
  34 flatten :: [[[a]]] -> [a]
  35 flatten xs = concat $ concat xs
  36
  37
  38 -- | Switch the x and z dimensions of a three-dimensional list.
  39 transpose_xz :: [[[a]]] -> [[[a]]]
  40 transpose_xz [] = []
  41 transpose_xz [[]] = [[]]
  42 transpose_xz [[[]]] = [[[]]]
  43 transpose_xz m =
  44     [[[ m !! x !! y !! z | x <- [0..xsize]]
  45                       | y <- [0..ysize]]
  46                       | z <- [0..zsize]]
  47     where
  48       zsize = (length m) - 1
  49       ysize = (length (m !! 0))- 1
  50       xsize = (length ((m !! 0) !! 0)) - 1
  51
  52 -- | Takes a list, and returns True if its elements are pairwise
  53 --   equal. Returns False otherwise.
  54 all_equal :: (Eq a) => [a] -> Bool
  55 all_equal xs =
  56     all (== first_element) other_elements
  57     where
  58       first_element  = head xs
  59       other_elements = tail xs