2016 Update

Task/Roman-numerals-Encode/Haskell/roman-numerals-encode-2.hs

@@ -1,2 +1,15 @@
-*Main> map toRoman [1999,25,944]
-["MCMXCIX","XXV","CMXLIV"]
+import Data.List (mapAccumL)
+
+roman :: Int -> String
+roman n = concatMap concat . snd $ mapAccumL tr n
+    [(1000, "M"), (900, "CM"), (500, "D") ,( 400, "CD"),
+     ( 100, "C"), ( 90, "XC") ,( 50, "L"), (  40, "XL"),
+     (  10, "X"), (  9, "IX"), (  5, "V"), (   4, "IV"),
+     (   1, "I")]
+  where
+    tr a (m, s) = (r, replicate q s)
+      where
+        (q, r) = quotRem a m
+
+main :: IO ()
+main = mapM_ (putStrLn . roman) [1666, 1990, 2008, 2016, 2017]

Task/Roman-numerals-Encode/Haskell/roman-numerals-encode.hs

@@ -1,13 +0,0 @@
-digit x y z k =
-  [[x],[x,x],[x,x,x],[x,y],[y],[y,x],[y,x,x],[y,x,x,x],[x,z]] !!
-  (fromInteger k - 1)
-
-toRoman :: Integer -> String
-toRoman 0 = ""
-toRoman x | x < 0     = error "Negative roman numeral"
-toRoman x | x >= 1000 = 'M' : toRoman (x - 1000)
-toRoman x | x >= 100  = digit 'C' 'D' 'M' q ++ toRoman r where
-  (q,r) = x `divMod` 100
-toRoman x | x >= 10   = digit 'X' 'L' 'C' q ++ toRoman r where
-  (q,r) = x `divMod` 10
-toRoman x             = digit 'I' 'V' 'X' x