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LLeeaarrnn yyoouu aa HHaasskkeellll

ffoorr GGrreeaatt GGoooodd!!

ZZiippppeerr

13年1月20日日曜日

WWhhoo??

•･島崎抄子•･ @@sshhookkooss•･ ccyybbeerraaggeenntt


IInnttrroodduuccttiioonn

TTrreeee→要素を気軽に変更

FFiillee SSyysstteemm→ファイルの操作


TTrreeee


TTrreeee

data Tree a = Empty | Node a (Tree a) (Tree a) deriving (Show)


TTrreeee

GGOOAALL::WW→PP


TTrreeeefreeTree :: Tree CharfreeTree = Node 'P' (Node 'O' (Node 'L' (Node 'N' Empty Empty) (Node 'T' Empty Empty) ) (Node 'Y' (Node 'S' Empty Empty) (Node 'A' Empty Empty) ) ) (Node 'L' (Node 'W' (Node 'C' Empty Empty) (Node 'R' Empty Empty) ) (Node 'A' (Node 'A' Empty Empty) (Node 'C' Empty Empty) ) )


TTrreeee

changeToP :: Tree Char -> Tree CharchangeToP (Node x l (Node y (Node _ m n) r)) =

　　　　Node x l (Node y (Node 'P' m n ) r)

RRiigghhtt→LLeefftt→PP


TTrreeee

進路をリストで指定→要素をPP

data Direction = L | R deriving (Show) type Directions = [Direction]

changeToP :: Directions -> Tree Char -> Tree Char

changeToP (L:ds) (Node x l r) = Node x (changeToP ds l) r changeToP (R:ds) (Node x l r) = Node x l (changeToP ds r) changeToP [] (Node _ l r) = Node 'P' l r


TTrreeee

elemAt :: Directions -> Tree a -> a

elemAt (L:ds) (Node _ l _) = elemAt ds l

elemAt (R:ds) (Node _ _ r) = elemAt ds r

elemAt [] (Node x _ _) = x

確認用目的地の要素を返す関数


TTrreeee

要素の更新を、何度も効率よくできるよう部分木から近場の部分木へ切り替えたい！


TTrreeee

道しるべを残すBBrreeaaddccrruummbbに辿った方向�を追加

type Breadcrumbs = [Direction]

goLeft :: (Tree a, Breadcrumbs) -> (Tree a, Breadcrumbs) goLeft (Node _ l _, bs) = (l, L:bs)

goRight :: (Tree a, Breadcrumbs) -> (Tree a, Breadcrumbs) goRight (Node _ _ r, bs) = (r, R:bs)


TTrreeee

( Node 'A' (Node 'A' Empty Empty) (Node 'C' Empty Empty) , [R, R]) :: (Tree a, Breadcrumbs)


TTrreeee

1133章で定義した x -: f = f x　を使い美�しく書ける

ghci> goLeft (goRight (freeTree, []))

!

ghci> (freeTree, []) -: goRight -: goLeft

実行結果：(Node 'W' (Node 'C' Empty Empty) (Node 'R' Empty Empty),[L,R])


TTrreeee

木の情報すべてを持ちたい！！！！


TTrreeee

辿らなかった部分木の情報も残す

data Crumb a = LeftCrumb a (Tree a) | RightCrumb a (Tree a)

　　　　deriving (Show)

type Breadcrumbs a = [Crumb a]

goLeft :: (Tree a, Breadcrumbs a) -> (Tree a, Breadcrumbs a) goLeft (Node x l r, bs) = (l, LeftCrumb x r:bs)

goRight :: (Tree a, Breadcrumbs a) -> (Tree a, Breadcrumbs a)

goRight (Node x l r, bs) = (r, RightCrumb x l:bs)


TTrreeee

情報がある→上へ戻れる！

goUp :: (Tree a, Breadcrumbs a) -> (Tree a, Breadcrumbs a) goUp (t, LeftCrumb x r:bs) = (Node x t r, bs)goUp (t, RightCrumb x l:bs) = (Node x l t, bs)


TTrreeee

TTrreeee aa と BBrreeaaddCCrruummbbのペアは、元の木の状態を持ちつつ、どの部分木に注目しているのかわかる！ZZiippppeerrで定義

type Zipper a = (Tree a, Breadcrumbs a)


TTrreeee注目している部分木のルートの書き換えができる

modify :: (a -> a) -> Zipper a -> Zipper a

modify f (Node x l r, bs)=(Node (f x ) l r, bs)

modify f (Empty, bs) = (Empty, bs)


TTrreeee

LLeefftt→RRiigghhtt→PPに要素を変更のあとに、ひとつ上の要素をXXに変更したい！

ghci> let newFocus =

(freeTree, []) -: goLeft -: goRight -: modify (\_ -> 'P')

ghci> let newFocus2 = newFocus -: goUp -: modify (\_ -> 'X')


TTrreeee

注目している部分木の置き換えもシンプルなコードでできる

attach :: Tree a -> Zipper a -> Zipper a

attach t (_, bs) = (t, bs)


TTrreeeeトップへ戻る

ggooUUppを、道しるべがなくなるまで再帰

topMost :: Zipper a -> Zipper a

topMost (t, []) = (t, [])

topMost z = topMost (goUp z)


LLiisstt

LLiissttをZZiippppeerrに！

（注目している要素、辿ってきた要素）


LLiisstt

LLiissttもZZiippppeerrで作ってみる！type ListZipper a = ([a], [a])

goForward :: ListZipper a -> ListZipper a

goForward (x:xs, bs) = (xs, x:bs)

goBack :: ListZipper a -> ListZipper a

goBack (xs, b:bs) = (b:xs, bs)


FFiillee SSyysstteemm


FFiillee SSyysstteemmtype Name = String

type Data = String

data FSItem = File Name Data | Folder Name [FSItem]

deriving (Show)

FFiillee・・・名前がついていて、データが入�っている

FFoollddeerr・・・名前がついていて、複数のファイルやフォルダをアイテムとして含む



myDisk :: FSItem

myDisk = Folder "root" [File "goat_yelling_like_man.wmv" "baaaaaa"

, File "pope_time.avi" "god bless"

, Folder "pics"

[File "ape_throwing_up.jpg" "bleargh"

, File "watermelon_smash.gif" "smash!!"

, File "skull_man(scary).bmp" "Yikes!"

]

, File "dijon_poupon.doc" "best mustard"

, Folder "programs"

[File "fartwizard.exe" "10gotofart"

, File "owl_bandit.dmg" "mov eax, h00t"

, File "not_a_virus.exe" "really not a virus"

, Folder "source code"

[File "best_hs_prog.hs" "main = print (fix error)"

, File "random.hs" "main = print 4"]

]

] 13年1月20日日曜日

Folder1

File2Folder2 File1

File3 Folder3

FFiilleeは空の木のようなもの



data FSCrumb = FSCrumb Name [FSItem] [FSItem] deriving (Show)

type FSZipper = (FSItem, [FSCrumb])

NNaammee::親フォルダ名[[FFSSIItteemm]]::前のアイテムのリスト　[[FFSSIItteemm]]::後ろのアイテムのリスト

（注目しているアイテム、道しるべのリスト）


Folder1

File2Folder2 File1

File3 Folder3

注目：FFoollddeerr11前のアイテム：FFoollddeerr22の情報等後ろのアイテム::なし



fsUp :: FSZipper -> FSZipperfsUp (item, FSCrumb name ls rs:bs) =

　　(Folder name (ls ++ [item] ++ rs), bs)

注目しているアイテムを、前のアイテムに移す

上の階層に行く


Folder1

File2Folder2 File1

File3 Folder3 注目：FFoollddeerr22前のアイテム：FFiillee33の情報等後ろのアイテム::FFoollddeerr11の情報等

注目：FFoollddeerr11前のアイテム：FFiillee22の情報等後ろのアイテム::なし



fsTo :: Name -> FSZipper -> FSZipper

fsTo name (Folder folderName items, bs) =

let (ls, item:rs) = break (nameIs name) items

in (item, FSCrumb folderName ls rs:bs)

nameIs :: Name -> FSItem -> BoolnameIs name (Folder folderName _) = name == folderName

nameIs name (File fileName _) = name == fileName

注目しているIItteemmを変更



fsRename :: Name -> FSZipper -> FSZipperfsRename newName (Folder name items, bs) = (Folder newName

items, bs)

fsRename newName (File name dat, bs) = (File newName dat, bs)

RReennaammee



fsNewFile :: FSItem -> FSZipper -> FSZipper

fsNewFile item (Folder folderName items, bs) =

(Folder folderName (item:items), bs)

NNeewwFFiillee


MMaayybbee!!!!!!goLeft :: Zipper a -> Maybe (Zipper a)

goLeft (Node x l r, bs) = Just (l, LeftCrumb x r:bs)

goLeft (Empty, _) = Nothing

goRight :: Zipper a -> Maybe (Zipper a)

goRight (Node x l r, bs) = Just (r, RightCrumb x l:bs)

goRight (Empty, _) = Nothing

goUp :: Zipper a -> Maybe (Zipper a)

goUp (t, LeftCrumb x r:bs) = Just (Node x t r, bs)

goUp (t, RightCrumb x l:bs) = Just (Node x l t, bs)

goUp (_, []) = Nothing


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