type command = [ `Roundtrip ]

let command_of_yojson = function
  | `String "Roundtrip" -> Ok `Roundtrip
  | _ -> Error "invalid command"

type request = { expr : string; command : command }
[@@deriving of_yojson { exn = true }]

type response = [ `Error of string ] [@@deriving to_yojson { exn = true }]

(*
type position = [%import: Lexing.position] [@@deriving show]

type location = [%import: (Location.t[@with Lexing.position := position])]
[@@deriving show]

type constant = [%import: Parsetree.constant] [@@deriving show]
type expression_desc = [%import: Parsetree.expression_desc] [@@deriving show]
type expression = [%import: Parsetree.expression] [@@deriving show]

type structure_item_desc = [%import: Parsetree.structure_item_desc]
[@@deriving show]

type structure_item = [%import: Parsetree.structure_item] [@@deriving show]
type structure = [%import: Parsetree.structure] [@@deriving show]
type toplevel_phrase = [%import: Parsetree.toplevel_phrase] [@@deriving show]

let parse ~path (src : string) =
  let buf = Lexing.from_string src in
  buf.lex_start_p <- { buf.lex_start_p with pos_fname = path };
  buf.lex_curr_p <- { buf.lex_curr_p with pos_fname = path };
  Parse.expression buf

let () =
  parse ~path:"main.ml" " print_endline ((\"Hello, world!\") )"
  |> Format.fprintf Format.std_formatter "\n%a\n" Pprintast.expression
*)

let handle_request { expr; command } : response =
  match command with `Roundtrip -> `Error ("TODO: " ^ expr)

let () =
  Yojson.Safe.from_channel stdin
  |> request_of_yojson_exn |> handle_request |> response_to_yojson
  |> Yojson.Safe.to_channel stdout