module HW7_2 where

import HW7_1

data Expr = Xml String [Expr]
         | Str String
  deriving Show

token p = do
    x <- p
    many whiteSpace
    return x

{-

  Xml ::= < Id > Body </ Id>
  Body ::= Xml* | String
  Id ::= identifier
  String ::= [^ '<']*  -- 0 or more characters which are not '<'

Examples:

   run xml "<a></a>"  ==>  Ok: Xml "a" []

   run xml "<a> hello <b> bye </b> </a>"  
   ==> 
       parse error at (column 10, line 0):
       unexpected <b
       expecting </a>

   run xml "<a> <b> hello </b> <c> bye </c> </a>"
   ==>
       Ok: Xml "a" [Xml "b" [Str "hello "],Xml "c" [Str "bye "]]

   run xml "<a> <b> hello </a> <c> bye </c> </a>"
   ==>
       parse error at (column 14, line 0):
       unexpected </a
       expecting </b>


White space shouldn't matter, so "< / a >" is equivalent to "</a>".
Don't worry about escape sequences in strings, i.e. "\\n"

-}

xml :: Parser Expr
xml =