Hello,

In order to implement a timers subsystem, I need a module with the 
following values:

*) add_timer : time -> ( unit -> unit ) -> timerid,
for public usage, where "add_timer t f" means execute "f" at time "t".  
The result is an identifier who allows cancelation of the timer.
*) cancel_timer: timerid -> unit
for public usage, cancel a previously added timer
*) peek_minimum_timer : unit -> ( time, unit -> unit )
for internal usage, get the timer with minimum time. Returns the time 
and the related function.
*) remove_minimum_timer : ?? -> unit
for internal usage, remove the timer with the minimum time. It will be 
called after execute a timer.

Thus, in a generic sense, what I need is a "sorted list", with easy 
insertion of elements, and peek/pop of the head (minimum).

Of the standard modules, the most similar seems "set", because allows 
insertion and has the funcion "min_elt". However, the problem is, if two 
timers have the same time, addition of the second one removes the first.

Please, has someone any sugestion?

Thanks a lot.