Data commit

Task/Test-integerness/Haskell/test-integerness-1.hs

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+import Data.Decimal
+import Data.Ratio
+import Data.Complex

Task/Test-integerness/Haskell/test-integerness-2.hs

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+class ContainsInteger a where
+  isInteger :: a -> Bool

Task/Test-integerness/Haskell/test-integerness-3.hs

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+instance ContainsInteger Int where isInteger _ = True
+instance ContainsInteger Integer where isInteger _ = True

Task/Test-integerness/Haskell/test-integerness-4.hs

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+isIntegerF :: (Eq x, RealFrac x) => x -> Bool
+isIntegerF x = x == fromInteger (truncate x)
+
+instance ContainsInteger Double where isInteger = isIntegerF
+instance Integral i => ContainsInteger (DecimalRaw i) where isInteger = isIntegerF
+instance Integral i => ContainsInteger (Ratio i) where isInteger = isIntegerF

Task/Test-integerness/Haskell/test-integerness-5.hs

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+instance (Eq a, Num a, ContainsInteger a) => ContainsInteger (Complex a) where
+  isInteger z = isInteger (realPart z) && (imagPart z == 0)

Task/Test-integerness/Haskell/test-integerness-6.hs

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+x ~~ eps = abs x <= eps
+
+almostInteger :: RealFrac a => a -> a -> Bool
+almostInteger eps x = (x - fromInteger (round x)) ~~ eps
+
+almostIntegerC :: RealFrac a => a -> Complex a -> Bool
+almostIntegerC eps z = almostInteger eps (realPart z) && (imagPart z) ~~ eps

Task/Test-integerness/Haskell/test-integerness-7.hs

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+tests = all (== True)
+  [ isInteger (5          :: Integer)
+  , isInteger (5.0        :: Decimal)
+  , isInteger (-5         :: Integer)
+  , isInteger (0          :: Decimal)
+  , isInteger (-2.1e120   :: Double)
+  , isInteger (5 % 1      :: Rational)
+  , isInteger (4 % 2      :: Rational)
+  , isInteger (5 :+ 0     :: Complex Integer)
+  , isInteger (5.0 :+ 0.0 :: Complex Decimal)
+  , isInteger (6 % 3 :+ 0 :: Complex Rational)
+  , isInteger (1/0        :: Double) -- Infinity is integer
+  , isInteger (1.1/0      :: Double) -- Infinity is integer
+  , not $ isInteger (5.01       :: Decimal)
+  , not $ isInteger (-5e-2      :: Double)
+  , not $ isInteger (5 % 3      :: Rational)
+  , not $ isInteger (5 :+ 1     :: Complex Integer)
+  , not $ isInteger (6 % 4 :+ 0 :: Complex Rational)
+  , not $ isInteger (5.0 :+ 1.0 :: Complex Decimal)
+  , almostInteger 0.01 2.001
+  , almostInteger 0.01 (-1.999999)
+  , almostInteger (1 % 10) (24 % 23)
+  , not $ almostInteger 0.01 2.02
+  , almostIntegerC 0.001 (5.999999 :+ 0.000001)
+  ]

Task/Test-integerness/Haskell/test-integerness-8.hs

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+pithagoreanTriangles :: [[Integer]]
+pithagoreanTriangles =
+  [ [a, b, round c] | b <- [1..]
+                    , a <- [1..b]
+                    , let c = sqrt (fromInteger (a^2 + b^2))
+                    , isInteger (c :: Double) ]