A-M baby

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

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+import Data.Ratio
+import Text.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 = do
+  -- Perform the mapping over floating point numbers.
+  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 n x = printf "%2d -> %6.3f\n" n x
+          prtR :: PrintfType r => Integer -> Rational -> r
+          prtR n x = printf "%2d -> %s\n" n (show x)