(*
   User Modes:
       +i  Invisible User Mode
       +o  Oper User Mode
       +w  WALLOPS User Mode

   Channel Modes:
     Type A:
       +b  Ban Channel Mode

     Type B:
       +k  Key Channel Mode
       +o  Operator Channel Membership Prefix (@)
       +v  Voice Channel Membership Prefix (+)

     Type C:
       +l  Client Limit Channel Mode

     Type D:
       +i  Invite-Only Channel Mode
       +m  Moderated Channel Mode
       +s  Secret Channel Mode
       +t  Protected Topic Channel Mode
       +n  No External Messages Mode
 *)

type user = [`i | `o | `w]
type chan_a = [`b]
type chan_b = [`k | `o | `v]
type chan_c = [`l]
type chan_d = [`i | `m | `s | `t | `n]
type chan = [chan_a | chan_b | chan_c | chan_d]
type t = [user | chan]

val pp : Format.formatter -> [< t] -> unit
val to_char : [< t] -> char
val of_char_user : char -> [> user]
val of_char_chan : char -> [> chan]