module Logger: Logger
type [ `Debug | `Error | `Fatal | `Info | `Warn ] * string 
type [ `Kb of int64 | `Mb of int64 | `Unlimited ] 
type 'messagetype t 
type message t 
val create : ?max_size:size ->
       ?mode:Core.Unix.file_perm ->
       ?max_archives:[ `Max of int | `Unlimited ] ->
       ?full_callback:(string Core.Std.Squeue.t -> unit) ->
       ?filter:('messagetype -> bool) ->
       message_to_string:('messagetype -> string) -> string -> 'messagetype t
- max_size - the maximum size of each log file (default 50Mb)
- mode - mode to open the files in
- max_archives - maximum number of archives to keep (default 4)
- full_callback - called when the logger queue backs up so far that log items
                    may have been lost.  Defaults to doing nothing.
- filter - if set, then every message is passed to filter before actually being
             logged.  If filter returns false the message is dropped.
- message_to_string - called to convert your message type to a string for logging
val create_default : ?max_size:size ->
       ?mode:Core.Unix.file_perm ->
       ?max_archives:[ `Max of int | `Unlimited ] ->
       ?full_callback:(string Core.Std.Squeue.t -> unit) ->
       string -> message t
creates a log using the default message type and a filter that drops 
  `Debug messages
val log : 'messagetype t -> 'messagetype -> unit
logs a message to log
val filter : 'messagetype t -> ('messagetype -> bool) -> unit
Sets the filter for a log
val clear_filter : 'messagetype t -> unit
removes the filter from a log
misc helper functions
val maybe_log : 'messagetype t option -> 'messagetype -> unit
logs a message to Some log, returns silently if log is None
val timestamp : unit -> string
Returns a timestamp as a string suitable for log files