src/Comparisons.hs

   1 -- | Functions for comparing 'Double' values.
   2 module Comparisons
   3 where
   4
   5 -- | epsilon is the value that will be used in all tests that require
   6 --   some measure of \"closeness.\" Increasing it will make those
   7 --   tests more tolerant.
   8 epsilon :: Double
   9 epsilon = 0.0001
  10
  11
  12 -- | x almost equals y if x is within 'epsilon' of y.
  13 almost_equals :: Double -> Double -> Bool
  14 almost_equals x y = (abs (x - y)) < epsilon
  15
  16 infix 4 ~=
  17 (~=) :: Double -> Double -> Bool
  18 (~=) = almost_equals
  19
  20
  21 -- | Like 'almost_equals', except much more tolerant. The difference
  22 --   between the two arguments must be less than one percent of the sum
  23 --   of their magnitudes.
  24 kinda_equals :: Double -> Double -> Bool
  25 kinda_equals x y =
  26     (abs (x - y)) < threshold
  27     where
  28       threshold = ((abs x) + (abs y)) / 100.0
  29
  30 infix 4 ~~=
  31 (~~=) :: Double -> Double -> Bool
  32 (~~=) = kinda_equals
  33
  34
  35 -- | x is very positive if it is 'epsilon' greater than zero.
  36 very_positive :: Double -> Bool
  37 very_positive x =  x - epsilon > 0
  38
  39
  40 -- | Takes a list of 'Double' and returns the ones which are not very
  41 --   positive.
  42 non_very_positive_entries :: [Double] -> [Double]
  43 non_very_positive_entries = filter (not . very_positive)