Put Mana into its own module

Magic.hs

@@ -1,41 +1,6 @@
 module Magic where
 
--------------------------------------------------------------------------------
--- Mana
--------------------------------------------------------------------------------
-
-data Color = Colorless
-    | Black
-    | White
-    | Red
-    | Blue
-    | Green
-    deriving (Show, Eq)
-
-data Mana = Mana Int Color
-    deriving (Show, Eq)
-
-data Cost = Cost [Mana]
-    deriving (Show, Eq)
-
-class ManaCost a where
-    converted :: a -> Int
-
-instance ManaCost Cost where
-    converted (Cost []) = 0
-    converted (Cost cost) = (foldl (\t (Mana x _) -> t + x) 0) cost
-
-color :: Color -> Cost -> Int
-color c (Cost cost) = converted (Cost (filter (\(Mana _ col) -> col == c) cost))
-
-pretty :: Cost -> String
-pretty c = concat ( [show (color Colorless c)
-    , replicate (color Black c) 'B'
-    , replicate (color White c) 'W'
-    , replicate (color Red   c) 'R'
-    , replicate (color Blue  c) 'U'
-    , replicate (color Green c) 'G'
-    ])
+import Mana
 
 -------------------------------------------------------------------------------
 -- Cards

Mana.hs

@@ -0,0 +1,42 @@
+module Mana where
+
+data Color = Colorless
+    | Black
+    | White
+    | Red
+    | Blue
+    | Green
+    deriving (Show, Eq)
+
+data Mana = Mana { amount :: Int
+                 , color  :: Color
+                 } deriving (Show, Eq)
+
+data Cost = Cost [Mana]
+    deriving (Eq)
+
+instance Show Cost where
+    show c = pretty c
+
+class ManaCost a where
+    converted :: a -> Int
+
+instance ManaCost Cost where
+    converted (Cost []) = 0
+    converted (Cost cost) = (foldl (\t (Mana x _) -> t + x) 0) cost
+
+pretty :: Cost -> String
+pretty c = do
+    let filtered c (Cost cost) = converted $ Cost $ filter (\x -> color x == c) cost
+    let colored = concat [ replicate (filtered Black c) 'B'
+                         , replicate (filtered White c) 'W'
+                         , replicate (filtered Red   c) 'R'
+                         , replicate (filtered Blue  c) 'U'
+                         , replicate (filtered Green c) 'G'
+                         ]
+    let colorless = filtered Colorless c
+    if length colored > 0 && colorless == 0 then
+        colored
+    else
+        (show colorless) ++ colored
+