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 tests
   7 --   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 -- | x is very positive if it is 'epsilon' greater than zero.
  22 very_positive :: Double -> Bool
  23 very_positive x =  x - epsilon > 0
  24
  25
  26 -- | Takes a list of 'Double' and returns the ones which are not very
  27 --   positive.
  28 non_very_positive_entries :: [Double] -> [Double]
  29 non_very_positive_entries = filter (not . very_positive)