exception Exc of string

(* File calc.ml *)
let rec ast_to_string ast = match ast with 
| Ast.Leaf s -> s
| Ast.Int i -> string_of_int i
| Ast.Node ls -> "[" ^ String.concat " " (List.map ast_to_string ls) ^ "]"
;;

(** interpreter for interp_int*)
class interp_int x_init =
    object (self)
      val mutable x = x_init
      method interp code = match code with
		| Ast.Int x -> x
		| Ast.Node [Ast.Leaf "+"; lhs; rhs] ->
			let x1 = self#interp lhs in
			let x2 = self#interp rhs in
			x1+x2 
		| Ast.Node [Ast.Leaf "-"; lhs; rhs] ->
			let x1 = self#interp lhs in
			let x2 = self#interp rhs in
			x1-x2 
		| Ast.Node [Ast.Leaf "-"; x] ->
			let x1 = self#interp x in
			0-x1 
		| Ast.Node [Ast.Leaf "%apply" ; Ast.Leaf "read"; Ast.Int 0] ->
			let input = read_int_opt () in
			match input with
			| Some(y) -> y
			| _ -> raise (Exc "input invalid number")
		| _ -> raise (Exc "unsupported")
    end;;




(**main body*)
        let _ =
          try
            let lexbuf = Lexing.from_channel stdin in
			let interp = new interp_int 0 in
            while true do
              let result = Parser.main Lexer.token lexbuf in
                Printf.printf "%d" (interp#interp result); print_newline(); flush stdout
            done
          with Lexer.Eof ->
            exit 0