parser.curry

import Char (isAlpha)
import List (intercalate)

type Name = [NameChar]
type NameChar = Char

nameChar2char :: Char -> NameChar
nameChar2char c | isAlpha c = c

name2str :: Name -> String
name2str = map nameChar2char

data Node = Node { nodeName :: Name
                 , attrs    :: [Attr]
                 , children :: [Node] }

data Attr = Attr { attrName :: Name
                 , value    :: String }

attr2string :: Attr -> String
attr2string (Attr name value) =
  name2str name ++ "=\"" ++ escape value ++ "\""
    where escape = concatMap (\c -> if c == '"' then "\\\"" else [c])

node2string :: Node -> String
node2string (Node name attrs children)
   | null children = "<" ++ name' ++ attrs' ++ "/>"
   | otherwise     = "<" ++ name' ++ attrs' ++ ">" ++ children' ++ "</" ++ name' ++ ">"
  where name'     = name2str name
        attrs'    = (concatMap ((" " ++) . attr2string) attrs)
        children' = intercalate "" $ map (node2string) children

inverse :: (a -> b) -> (b -> a)
inverse f y | f x =:= y = x where x free

parse :: String -> Node
parse = inverse node2string