Haskell - 文字列(文字のリスト)のリスト(辞書順ソート(小文字化(Data.CharモジュールのtoLower関数))))

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 Lion - Apple(OS)
• Emacs、BBEdit - Bare Bones Software, Inc. (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)

『初めてのプログラミング 第2版』(Chris Pine 著、長尾 高弘 訳、オライリー・ジャパン、2010年、ISBN978-4-87311-469-9)の10章(章全部で復習), 10.3(練習問題)、辞書順ソートを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)

辞書順ソート(小文字化(Data.CharモジュールのtoLower関数))

コード(BBEdit)

sample.hs

{-# OPTIONS -Wall -Werror #-}

import qualified Data.Char as Char

main :: IO ()
main = do
    let langs :: [String]
        langs = ["ruby", "python", "dart", "haskell", "c", 
                 "scheme", "lisp", "csharp", "cpp", "perl",
                 "Ruby", "Python", "Dart", "Haskell", "C",
                 "Scheme", "Lisp", "CSharp", "CPP", "Perl"]
        sorted_langs = sort langs
    putStrLn $ "ソート前: " ++ (show $ langs)
    putStrLn $ "ソート後: " ++ (show $ sorted_langs)


sort :: [String] -> [String]
sort [] = []
sort xs =
    let myMinString :: [String] -> String
        myMinString [] = []
        myMinString (y:[]) = y
        myMinString (y:z:ys) = if myMin y z
                               then myMinString (y:ys)
                               else myMinString (z:ys)
        myMin :: String -> String -> Bool
        myMin [] _ = True
        myMin _ [] = False
        myMin (u:us) (t:ts)
            | (Char.toLower u) < (Char.toLower t) = True
            | (Char.toLower u) > (Char.toLower t) = False
            | otherwise = myMin us ts
        remove :: [String] -> String -> [String]
        remove (v:vs) w = if v == w
                          then vs
                          else v:remove vs w
        remove _ _ = []
        
        a = myMinString xs
    in a:(sort $ remove xs a)

入出力結果(Terminal, runghc)

$ runghc sample.hs
ソート前: ["ruby","python","dart","haskell","c","scheme","lisp","csharp","cpp","perl","Ruby","Python","Dart","Haskell","C","Scheme","Lisp","CSharp","CPP","Perl"]
ソート後: ["c","C","cpp","CPP","csharp","CSharp","dart","Dart","haskell","Haskell","lisp","Lisp","perl","Perl","python","Python","ruby","Ruby","scheme","Scheme"]
$