zippers.hs

-- filesystem

type Name = String
type Data = String
data FSItem = File Name Data | Folder Name [FSItem] deriving (Show)

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"  
                ]  
            ]  
        ]

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

type FSZipper = (FSItem, [FSCrumb])

fsUp :: FSZipper -> FSZipper
fsUp (item, FSCrumb name ls rs:bs) = (Folder name (ls ++ [item] ++ rs), bs)



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 -> Bool
nameIs name (Folder folderName _) = name == folderName
nameIs name (File fileName _) = name == fileName

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

fsNewFile :: FSItem -> FSZipper -> FSZipper
fsNewFile item (Folder folderName items, bs) =
    (Folder folderName (item:items), bs)