Haskell - Data.Mapモジュール(fromList, elems 関数(バランス色))

すごいHaskellたのしく学ぼう!
(オーム社)
Miran Lipovača (著)
田中 英行 村主 崇行 (翻訳)
[Kindle版]

開発環境

• OS X Mavericks - Apple(OS)
• BBEdit - Bare Bones Software, Inc., Emacs (Text Editor)
• Haskell (純粋関数型プログラミング言語)
• GHC (The Glasgow Haskell Compiler) (処理系)
• The Haskell Platform (インストール方法、モジュール等)

初めてのコンピュータサイエンス(Jennifer Campbell、Paul Gries、Jason Montojo、Greg Wilson(著)長尾 高弘(翻訳))の9章(集合と辞書)、9.5(練習問題)、8.をHaskellで解いてみる。

その他参考書籍

• プログラミングHaskell (オーム社) Graham Hutton(著) 山本 和彦(翻訳)
• Real World Haskell―実戦で学ぶ関数型言語プログラミング (オライリージャパン) Bryan O'Sullivan John Goerzen Don Stewart(著) 山下 伸夫 伊東 勝利 株式会社タイムインターメディア(翻訳)

9.5(練習問題)、8.

コード(BBEdit)

Sample.hs

{-# OPTIONS -Wall -Werror #-}
import qualified Data.Map as Map
import System.Random    

main :: IO ()
main = mapM_ putStrLn $ map (\x -> show x ++ ": " ++ (show $ isBalanced x)) $
                            map colorMap $ take 50 [0..]
    
isBalanced :: (Num a, Eq a) => Map.Map k a -> Bool
isBalanced m = if sum (Map.elems m) == 1 then True else False

colorMap :: Int -> Map.Map Char Double
colorMap n = Map.fromList $ zip ['R', 'G', 'B'] $
    map (\x -> (fromIntegral x :: Double) / (10.0 :: Double)) $
        take 3 $ randomRs ((1 :: Int), (5 :: Int)) (mkStdGen n)

入出力結果(Terminal, runghc)

$ runghc Sample.hs
fromList [('B',0.1),('G',0.1),('R',0.1)]: False
fromList [('B',0.3),('G',0.4),('R',0.3)]: True
fromList [('B',0.3),('G',0.2),('R',0.2)]: False
fromList [('B',0.5),('G',0.1),('R',0.1)]: False
fromList [('B',0.2),('G',0.1),('R',0.5)]: False
fromList [('B',0.2),('G',0.4),('R',0.4)]: True
fromList [('B',0.4),('G',0.2),('R',0.3)]: False
fromList [('B',0.1),('G',0.1),('R',0.2)]: False
fromList [('B',0.1),('G',0.1),('R',0.1)]: False
fromList [('B',0.3),('G',0.4),('R',0.5)]: False
fromList [('B',0.3),('G',0.2),('R',0.4)]: False
fromList [('B',0.5),('G',0.1),('R',0.3)]: False
fromList [('B',0.2),('G',0.1),('R',0.2)]: False
fromList [('B',0.2),('G',0.4),('R',0.1)]: False
fromList [('B',0.4),('G',0.2),('R',0.5)]: False
fromList [('B',0.1),('G',0.1),('R',0.4)]: False
fromList [('B',0.1),('G',0.1),('R',0.3)]: False
fromList [('B',0.3),('G',0.4),('R',0.2)]: False
fromList [('B',0.3),('G',0.2),('R',0.1)]: False
fromList [('B',0.5),('G',0.1),('R',0.5)]: False
fromList [('B',0.2),('G',0.1),('R',0.4)]: False
fromList [('B',0.2),('G',0.4),('R',0.3)]: False
fromList [('B',0.4),('G',0.2),('R',0.2)]: False
fromList [('B',0.1),('G',0.1),('R',0.1)]: False
fromList [('B',0.1),('G',0.1),('R',0.5)]: False
fromList [('B',0.3),('G',0.4),('R',0.4)]: False
fromList [('B',0.3),('G',0.2),('R',0.3)]: False
fromList [('B',0.5),('G',0.1),('R',0.2)]: False
fromList [('B',0.2),('G',0.1),('R',0.1)]: False
fromList [('B',0.2),('G',0.4),('R',0.5)]: False
fromList [('B',0.4),('G',0.2),('R',0.4)]: True
fromList [('B',0.1),('G',0.1),('R',0.3)]: False
fromList [('B',0.1),('G',0.1),('R',0.2)]: False
fromList [('B',0.3),('G',0.4),('R',0.1)]: False
fromList [('B',0.3),('G',0.2),('R',0.5)]: True
fromList [('B',0.5),('G',0.1),('R',0.4)]: True
fromList [('B',0.2),('G',0.1),('R',0.3)]: False
fromList [('B',0.2),('G',0.4),('R',0.2)]: False
fromList [('B',0.4),('G',0.2),('R',0.1)]: False
fromList [('B',0.1),('G',0.1),('R',0.5)]: False
fromList [('B',0.1),('G',0.1),('R',0.4)]: False
fromList [('B',0.3),('G',0.4),('R',0.3)]: True
fromList [('B',0.3),('G',0.2),('R',0.2)]: False
fromList [('B',0.5),('G',0.1),('R',0.1)]: False
fromList [('B',0.2),('G',0.1),('R',0.5)]: False
fromList [('B',0.2),('G',0.4),('R',0.4)]: True
fromList [('B',0.4),('G',0.2),('R',0.3)]: False
fromList [('B',0.1),('G',0.1),('R',0.2)]: False
fromList [('B',0.1),('G',0.1),('R',0.1)]: False
fromList [('B',0.3),('G',0.4),('R',0.5)]: False
$

{-# OPTIONS -Wall -Werror #-}を記述してるから、細かく型を指定(:: Double)しないと警告がいっぱい出た。慣れるまでは{-# OPTIONS -Wall -Werror #-}の記述を消さずに細かく型を指定していくことに。