Data commit

Task/Map-range/Haskell/map-range.hs

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+import Data.Ratio
+import Text.Printf (PrintfType, printf)
+
+-- Map a value from the range [a1,a2] to the range [b1,b2].  We don't check
+-- for empty ranges.
+mapRange
+  :: Fractional a
+  => (a, a) -> (a, a) -> a -> a
+mapRange (a1, a2) (b1, b2) s = b1 + (s - a1) * (b2 - b1) / (a2 - a1)
+
+main :: IO ()
+main
+-- Perform the mapping over floating point numbers.
+ = do
+  putStrLn "---------- Floating point ----------"
+  mapM_ (\n -> prtD n . mapRange (0, 10) (-1, 0) $ fromIntegral n) [0 .. 10]
+  -- Perform the same mapping over exact rationals.
+  putStrLn "---------- Rationals ----------"
+  mapM_ (\n -> prtR n . mapRange (0, 10) (-1, 0) $ n % 1) [0 .. 10]
+  where
+    prtD
+      :: PrintfType r
+      => Integer -> Double -> r
+    prtD = printf "%2d -> %6.3f\n"
+    prtR
+      :: PrintfType r
+      => Integer -> Rational -> r
+    prtR n x = printf "%2d -> %s\n" n (show x)