すごいH本読書会 in 大阪 #5

gistfile1.hs

data Bookmark = Bookmark { name :: String, url :: String } |
            Folder { name :: String, children :: [Bookmark] } deriving (Show, Eq)

root = Folder "root" [(Bookmark "sample1" "http://example.com"),
                      (Bookmark "sample2" "http://example.com"),
                      (Bookmark "sample3" "http://example.com")]
emptyChildren = Folder "root" []
recursibleFolder = Folder "root" [(Bookmark "sample1" "http://example.com"),
                                  root]

toJson :: Bookmark -> String
toJson (Bookmark name url) = "{\"name\":\"" ++ name ++ "\",\"URL\":\"" ++ url ++ "\"}"
toJson (Folder name children) = "{\"name\":\"" ++ name ++ "\",\"children\":[" ++ toString children ++ "]}"
        where toString xs = trancate $ foldr (\b acc -> toJson b ++ "," ++ acc) "" xs
              trancate xs
                  | xs == [] = ""
                  | otherwise = init xs

addBookmark :: Bookmark -> Bookmark -> Bookmark
addBookmark (Folder n c) b = Folder n (b:c)
addBookmark b _ = b