git.kianting.info Git - uann/blob - ocaml_yacc/calc.ml

   1 exception Exc of string
   2
   3 (* File calc.ml *)
   4 let rec ast_to_string ast = match ast with
   5 | Ast.Leaf s -> s
   6 | Ast.Int i -> string_of_int i
   7 | Ast.Node ls -> "[" ^ String.concat " " (List.map ast_to_string ls) ^ "]"
   8 ;;
   9
  10 (** interpreter for interp_int*)
  11 class interp_int x_init =
  12     object (self)
  13       val mutable x = x_init
  14       method interp code = match code with
  15                 | Ast.Int x -> x
  16                 | Ast.Node [Ast.Leaf "+"; lhs; rhs] ->
  17                         let x1 = self#interp lhs in
  18                         let x2 = self#interp rhs in
  19                         x1+x2
  20                 | Ast.Node [Ast.Leaf "-"; lhs; rhs] ->
  21                         let x1 = self#interp lhs in
  22                         let x2 = self#interp rhs in
  23                         x1-x2
  24                 | Ast.Node [Ast.Leaf "-"; x] ->
  25                         let x1 = self#interp x in
  26                         0-x1
  27                 | Ast.Node [Ast.Leaf "%apply" ; Ast.Leaf "read"; Ast.Int 0] ->
  28                         let input = read_int_opt () in
  29                         match input with
  30                         | Some(y) -> y
  31                         | _ -> raise (Exc "input invalid number")
  32                 | _ -> raise (Exc "unsupported")
  33     end;;
  34
  35
  36
  37
  38 (**main body*)
  39         let _ =
  40           try
  41             let lexbuf = Lexing.from_channel stdin in
  42                         let interp = new interp_int 0 in
  43             while true do
  44               let result = Parser.main Lexer.token lexbuf in
  45                 Printf.printf "%d" (interp#interp result); print_newline(); flush stdout
  46             done
  47           with Lexer.Eof ->
  48             exit 0
  49
  50