import Matcher;

local m = initMatcher ("   -- asdasdakm ,m.,msd .,m.,asd\n    \n\n abc");

local
  lident  = createRegexp ("[a-z][a-zA-Z_]*", "lowercase identifier"),
  uident  = createRegexp ("[A-Z][a-zA-Z_]*", "uppercase identifier"),
  ws      = createRegexp ("\\([ \t\n]\\|--[^\n]*\n\\)*", "whitespace"),
  str     = createRegexp ("""\([^""]\|""""\)*""", "string literal"),
  decimal = createRegexp ("[0-9]+", "decimal literal"),
  chr     = createRegexp ("'[^']'", "character literal");

fun token (s) {
  fun (m) {m.matchString (s)}
}

fun lid (m) {
  matchRegexp (m, lident)
}

fun uid (m) {
  matchRegexp (m, uident)
}

fun const (m) {
  matchRegexp (m, decimal)
}

infixl @ before * (p, f) {
  fun (m) {    
    case p (m) of
      Succ (x, m) -> Succ (f (x), m)
    | err         -> err
    esac
  }
}

infixr |> after !! (l, r) {
  fun (m) {
    case l (m) of
      Succ (s, m) -> r (s) (m)
    | err         -> err
    esac
  }
}

infixr || after |> (l, r) {
  fun (m) {  
    case l (m) of
      s@Succ (_, _) -> s 
    | err           -> r (m)
    esac
  }
}

local expr = lid @ fun (s) {Lid (s)} || const @ fun (s) {Dec (s)},
      assn = lid |> fun (id) {token (":=") |> fun (s) {expr @ fun (e) {Assn (id, e)}}};

printf ("%s\n", case assn (initMatcher ("x:=3")) of Fail (err) -> err | Succ (s, _) -> s.string esac)