val logf : int ‑> ((('a, Format.formatter, unit, unit, unit, unit) Pervasives.format6 ‑> 'a) ‑> unit) ‑> unit
Log at the given level, using a Format-ready message. This is
designed to be cheap if the message won't be printed because its
level is too high.
Use like this:
logf 1 (fun k->k "hello %s, 42=%d" "world" (41+1))
val default_logger : logger
val set_logger : logger ‑> unit