Haskell Night: LT モナドで作る正規表現コンビネータライブラリ

Sep 3, 20130 likes899 views

Akihiro Harai

2009年11月20日に行われた「Haskell Night」において発表されたスライド。

自己紹介
Haskell を知ったのは
「ふつける」が出る半年くらい前
2005 年末くらい？
Java で必ず final を付ける
自分の性格によくマッチ
原井彰弘（はらいあきひろ）

きっかけその 1
内部 DSL では
無理？
GHC 付属の正規表現ライブラリが
正規表現を「文字列」として扱うことに不満

きっかけその 2
Yet Another Haskell Tutorial
Chapter 9 "Monads" 119 ページ
「 Haskell のグルになりたい者のみモナドを作れ」
「されど、モナドの作り方が分かれば Haskell ライフ
はより豊かになるだろう」

モナドを使って
Parsec っぽい
正規表現コンビネータを作れば
一挙両得？？

モナドの能力的に可能か？
バックトラックは？
後方参照は？
従来型 NFA ならば
リストと遅延評価を使って自然に書ける
言語内 DSL のメリットを生かせば
自由自在

こんな感じに使います
testRegex :: Regex ()
testRegex = do
rxCaret
(matched, val) <- rxStar $
do
rxOneChar 'a'
rxOneChar 'b'
rxOneChar 'c'
rxOneChar 'd'
rxDollar
return ()
わかりやすさ重視のため
冗長性には目をつぶってください???
/^(ab)*cd
$/
rxStar 以下で
マッチした文字列
rxStar から返される
任意の値

メリットとデメリット
メリット
デメリット
強い静的型付け
表現の再利用が容易
表現の動的な作成と変更が可能
（文字列ではなく）任意のトークン列への
適用が可能（未実装）
記述が冗長
最適化は Haskell コンパイラ依存

実装（一部）
newtype Regex a =
Rx { runRegex :: (RxTarget -> [(RxTarget,
a)]) }
data RxTarget = RxTarget {
rxTargetBefore :: String, -- 逆順
rxTargetMatched :: String, -- 逆順
rxTargetAfter :: String }
instance Monad Regex where
m >>= next = Rx $ target -> let
thisCand = runRegex m target
getNextCand (target', a) = runRegex (next a) tar
get'
in concatMap getNextCand thisCand
return a = Rx $ target -> [(target, a)]

実装ずみの機能
^ $ * ( ) *? . |
[ ]
後方参照など
モナドで全部できる！

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Haskell Night: LT モナドで作る正規表現コンビネータライブラリ

1. モナドで作る正規表現コンビネータライブラリ Akihiro HARAI

2. 自己紹介 Haskell を知ったのは「ふつける」が出る半年くらい前 2005 年末くらい？ Java で必ず final を付ける自分の性格によくマッチ原井彰弘（はらいあきひろ）

3. モナドを使った正規表現コンビネータライブラリ

4. きっかけその 1 内部 DSL では無理？ GHC 付属の正規表現ライブラリが正規表現を「文字列」として扱うことに不満

5. きっかけその 2 Yet Another Haskell Tutorial Chapter 9 "Monads" 119 ページ「 Haskell のグルになりたい者のみモナドを作れ」「されど、モナドの作り方が分かれば Haskell ライフはより豊かになるだろう」

6. モナドを使って Parsec っぽい正規表現コンビネータを作れば一挙両得？？

7. モナドの能力的に可能か？バックトラックは？後方参照は？

8. モナドの能力的に可能か？バックトラックは？後方参照は？従来型 NFA ならばリストと遅延評価を使って自然に書ける言語内 DSL のメリットを生かせば自由自在

9. こんな感じに使います testRegex :: Regex () testRegex = do rxCaret (matched, val) <- rxStar $ do rxOneChar 'a' rxOneChar 'b' rxOneChar 'c' rxOneChar 'd' rxDollar return () わかりやすさ重視のため冗長性には目をつぶってください??? /^(ab)*cd $/ rxStar 以下でマッチした文字列 rxStar から返される任意の値

10. 実演

11. メリットとデメリットメリットデメリット強い静的型付け表現の再利用が容易表現の動的な作成と変更が可能（文字列ではなく）任意のトークン列への適用が可能（未実装）記述が冗長最適化は Haskell コンパイラ依存

12. 実装（一部） newtype Regex a = Rx { runRegex :: (RxTarget -> [(RxTarget, a)]) } data RxTarget = RxTarget { rxTargetBefore :: String, -- 逆順 rxTargetMatched :: String, -- 逆順 rxTargetAfter :: String } instance Monad Regex where m >>= next = Rx $ target -> let thisCand = runRegex m target getNextCand (target', a) = runRegex (next a) tar get' in concatMap getNextCand thisCand return a = Rx $ target -> [(target, a)]

13. 実装ずみの機能 ^ $ * ( ) *? . | [ ] 後方参照などモナドで全部できる！

14. モナドってすごい！ Haskell ってすごい！

15. ご清聴ありがとうございました

狠狠撸

Haskell Night: LT モナドで作る正規表現コンビネータライブラリ

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