datatype token =    Key of string  | Name of string; exception SynError of string; fun $a (Key b :: toks) =      if a=b then (a, toks) else raise SynError a  | $a _ =      raise SynError "Symbol expected"; fun id (Name a :: toks) = (a, toks)  | id toks = raise SynError "Identifier expected"; infix 3 >>; fun (ph >> f) toks =      let val (x, toks') = ph toks      in  (f x, toks') end; infix 0 ||; fun (ph1 || ph2) toks =      ph1 toks handle SynError _ => ph2 toks; infix 5 ~~; fun (ph1 ~~ ph2) toks =      let val (x, toks1) = ph1 toks          val (y, toks2) = ph2 toks1      in ((x,y), toks2) end; fun empty toks = ([], toks); fun many ph toks =      ( ph ~~ many ph >> (op ::) || empty ) toks; fun snd (_, y) = y; fun many_sep ph sep toks =      ( ph ~~ ( (sep ~~ many_sep ph sep >> snd) || empty ) >> (op ::) ) toks; fun parser ph toks =      (case ph toks         of (x, [])   => x          | (_, _::_) => raise SynError "Extra characters in phrase"      ); datatype typ  = Con of string * typ list  | Var of string; local  fun typ toks =    (   atom ~~ $"->" ~~ typ   >> (fn ((S, _), T) => Con("->", [S,T]))    ||  atom    ) toks  and atom toks =    (   id                     >> Var    ||  $"(" ~~ typ ~~ $")"    >> (fn ((_, T), _) => T)  ) toks;in  val parseTypeExp = parser typ;end; val t1 = [Name "a", Key "->", Name "b", Key "->", Name "c"];val t2 = [Key "(", Name "a", Key "->", Name "b", Key ")", Key "->", Name "c"];parseTypeExp t1;parseTypeExp t2;