2016 Update

Task/Temperature-conversion/Haskell/temperature-conversion-2.hs

@@ -0,0 +1,24 @@
+{-# LANGUAGE LambdaCase #-}
+
+import System.Exit (die)
+import Control.Monad (mapM_)
+import Control.Error.Safe (tryAssert, tryRead)
+import Control.Monad.Trans (liftIO)
+import Control.Monad.Trans.Except
+
+main = putStrLn "Please enter temperature in kelvin: " >>
+       runExceptT getTemp >>=
+       \case Right x  -> mapM_ putStrLn $ convert x
+             Left err -> die err
+
+convert :: Double -> [String]
+convert n = zipWith (++) labels nums
+    where labels      = ["kelvin: ", "celcius: ", "farenheit: ", "rankine: "]
+          conversions = [id, subtract 273, subtract 459.67 . (1.8 *), (1.8 *)]
+          nums        = (show . ($ n)) <$> conversions
+
+getTemp :: ExceptT String IO Double
+getTemp = do
+    t <- liftIO getLine >>= tryRead "Could not read temp"
+    tryAssert "Temp cannot be negative" (t>=0)
+    return t