type t =
  | Int of int
  | Ident of string
  | Plus
  | Minus
  | Asterisk
  | Slash
  | Carret
  | Percent
  | LParen
  | RParen

let of_char = function
  | '+' -> Plus
  | '-' -> Minus
  | '*' -> Asterisk
  | '/' -> Slash
  | '^' -> Carret
  | '%' -> Percent
  | '(' -> LParen
  | ')' -> RParen
  | _ -> invalid_arg "Token.of_char"

let of_string str =
  let fc = Char.code str.[0] in
  if Char.(code '0' <= fc && fc <= code '9') then
    Int (int_of_string str)
  else
    match str with
    | _ when String.length str = 1 -> of_char str.[0]
    | _ -> failwith "Token.of_string"

let to_string = function
  | Int n -> string_of_int n
  | Ident s -> s
  | Plus -> "+"
  | Minus -> "-"
  | Asterisk -> "*"
  | Slash -> "/"
  | Carret -> "^"
  | Percent -> "%"
  | LParen -> "("
  | RParen -> ")"