+(** 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*)