module Printexc: Printexctypet =exn= ..
The type of exception values.
val to_string : exn -> stringPrintexc.to_string e returns a string representation of
   the exception e.
val to_string_default : exn -> stringPrintexc.to_string_default e returns a string representation of the
    exception e, ignoring all registered exception printers.
val print : ('a -> 'b) -> 'a -> 'bPrintexc.print fn x applies fn to x and returns the result.
   If the evaluation of fn x raises any exception, the
   name of the exception is printed on standard error output,
   and the exception is raised again.
   The typical use is to catch and report exceptions that
   escape a function application.
val catch : ('a -> 'b) -> 'a -> 'bPrintexc.catch fn x is similar to Printexc.print, but
   aborts the program with exit code 2 after printing the
   uncaught exception.  This function is deprecated: the runtime
   system is now able to print uncaught exceptions as precisely
   as Printexc.catch does.  Moreover, calling Printexc.catch
   makes it harder to track the location of the exception
   using the debugger or the stack backtrace facility.
   So, do not use Printexc.catch in new code.
val print_backtrace : out_channel -> unitPrintexc.print_backtrace oc prints an exception backtrace
    on the output channel oc.  The backtrace lists the program
    locations where the most-recently raised exception was raised
    and where it was propagated through function calls.
If the call is not inside an exception handler, the returned backtrace is unspecified. If the call is after some exception-catching code (before in the handler, or in a when-guard during the matching of the exception handler), the backtrace may correspond to a later exception than the handled one.
val get_backtrace : unit -> stringPrintexc.get_backtrace () returns a string containing the
    same exception backtrace that Printexc.print_backtrace would
    print. Same restriction usage than Printexc.print_backtrace.
val record_backtrace : bool -> unitPrintexc.record_backtrace b turns recording of exception backtraces
    on (if b = true) or off (if b = false).  Initially, backtraces
    are not recorded, unless the b flag is given to the program
    through the OCAMLRUNPARAM variable.
val backtrace_status : unit -> boolPrintexc.backtrace_status() returns true if exception
    backtraces are currently recorded, false if not.
val register_printer : (exn -> string option) -> unitPrintexc.register_printer fn registers fn as an exception
    printer.  The printer should return None or raise an exception
    if it does not know how to convert the passed exception, and Some with 
    ss the resulting string if it can convert the passed
    exception. Exceptions raised by the printer are ignored.
When converting an exception into a string, the printers will be invoked
    in the reverse order of their registrations, until a printer returns
    a Some s value (if no such printer exists, the runtime will use a
    generic printer).
When using this mechanism, one should be aware that an exception backtrace
    is attached to the thread that saw it raised, rather than to the exception
    itself. Practically, it means that the code related to fn should not use
    the backtrace if it has itself raised an exception before.
val use_printers : exn -> string optionPrintexc.use_printers e returns None if there are no registered
    printers and Some s with else as the resulting string otherwise.
type 
The type raw_backtrace stores a backtrace in a low-level format,
    which can be converted to usable form using raw_backtrace_entries
    and backtrace_slots_of_raw_entry below.
Converting backtraces to backtrace_slots is slower than capturing the
    backtraces. If an application processes many backtraces, it can be useful
    to use raw_backtrace to avoid or delay conversion.
Raw backtraces cannot be marshalled. If you need marshalling, you
    should use the array returned by the backtrace_slots function of
    the next section.
typeraw_backtrace_entry = privateint
A raw_backtrace_entry is an element of a raw_backtrace.
Each raw_backtrace_entry is an opaque integer, whose value is not stable
    between different programs, or even between different runs of the same
    binary.
A raw_backtrace_entry can be converted to a usable form using
    backtrace_slots_of_raw_entry below. Note that, due to inlining, a
    single raw_backtrace_entry may convert to several backtrace_slots.
    Since the values of a raw_backtrace_entry are not stable, they cannot
    be marshalled. If they are to be converted, the conversion must be done
    by the process that generated them.
Again due to inlining, there may be multiple distinct raw_backtrace_entry
    values that convert to equal backtrace_slots. However, if two
    raw_backtrace_entrys are equal as integers, then they represent the same
    backtrace_slots.
val raw_backtrace_entries : raw_backtrace -> raw_backtrace_entry arrayval get_raw_backtrace : unit -> raw_backtracePrintexc.get_raw_backtrace () returns the same exception
    backtrace that Printexc.print_backtrace would print, but in
    a raw format. Same restriction usage than Printexc.print_backtrace.
val print_raw_backtrace : out_channel -> raw_backtrace -> unitPrint a raw backtrace in the same format
    Printexc.print_backtrace uses.
val raw_backtrace_to_string : raw_backtrace -> stringReturn a string from a raw backtrace, in the same format
    Printexc.get_backtrace uses.
val raise_with_backtrace : exn -> raw_backtrace -> 'aReraise the exception using the given raw_backtrace for the origin of the exception
val get_callstack : int -> raw_backtracePrintexc.get_callstack n returns a description of the top of the
    call stack on the current program point (for the current thread),
    with at most n entries.  (Note: this function is not related to
    exceptions at all, despite being part of the Printexc module.)
val default_uncaught_exception_handler : exn -> raw_backtrace -> unitPrintexc.default_uncaught_exception_handler prints the exception and
    backtrace on standard error output.
val set_uncaught_exception_handler : (exn -> raw_backtrace -> unit) -> unitPrintexc.set_uncaught_exception_handler fn registers fn as the handler
    for uncaught exceptions. The default handler is
    Printexc.default_uncaught_exception_handler.
Note that when fn is called all the functions registered with
    at_exit have already been called. Because of this you must
    make sure any output channel fn writes on is flushed.
Also note that exceptions raised by user code in the interactive toplevel are not passed to this function as they are caught by the toplevel itself.
If fn raises an exception, both the exceptions passed to fn and raised
    by fn will be printed with their respective backtrace.
These functions are used to traverse the slots of a raw backtrace and extract information from them in a programmer-friendly format.
type 
The abstract type backtrace_slot represents a single slot of
    a backtrace.
val backtrace_slots : raw_backtrace -> backtrace_slot array optionReturns the slots of a raw backtrace, or None if none of them
    contain useful information.
In the return array, the slot at index 0 corresponds to the most
    recent function call, raise, or primitive get_backtrace call in
    the trace.
Some possible reasons for returning None are as follow:
-g)ocamlc -g)val backtrace_slots_of_raw_entry : raw_backtrace_entry -> backtrace_slot array optionReturns the slots of a single raw backtrace entry, or None if this
    entry lacks debug information.
Slots are returned in the same order as backtrace_slots: the slot
    at index 0 is the most recent call, raise, or primitive, and
    subsequent slots represent callers.
type |    | filename :  | 
|    | line_number :  | 
|    | start_char :  | 
|    | end_char :  | 
}
The type of location information found in backtraces. start_char
    and end_char are positions relative to the beginning of the
    line.
module Slot:sig..end
type 
This type is used to iterate over the slots of a raw_backtrace.
    For most purposes, backtrace_slots_of_raw_entry is easier to use.
Like raw_backtrace_entry, values of this type are process-specific and
    must absolutely not be marshalled, and are unsafe to use for this reason
    (marshalling them may not fail, but un-marshalling and using the result
    will result in undefined behavior).
Elements of this type can still be compared and hashed: when two elements are equal, then they represent the same source location (the converse is not necessarily true in presence of inlining, for example).
val raw_backtrace_length : raw_backtrace -> intraw_backtrace_length bckt returns the number of slots in the
    backtrace bckt.
val get_raw_backtrace_slot : raw_backtrace -> int -> raw_backtrace_slotget_raw_backtrace_slot bckt pos returns the slot in position pos in the
    backtrace bckt.
val convert_raw_backtrace_slot : raw_backtrace_slot -> backtrace_slotExtracts the user-friendly backtrace_slot from a low-level
    raw_backtrace_slot.
val get_raw_backtrace_next_slot : raw_backtrace_slot -> raw_backtrace_slot optionget_raw_backtrace_next_slot slot returns the next slot inlined, if any.
Sample code to iterate over all frames (inlined and non-inlined):
      (* Iterate over inlined frames *)
      let rec iter_raw_backtrace_slot f slot =
        f slot;
        match get_raw_backtrace_next_slot slot with
        | None -> ()
        | Some slot' -> iter_raw_backtrace_slot f slot'
      (* Iterate over stack frames *)
      let iter_raw_backtrace f bt =
        for i = 0 to raw_backtrace_length bt - 1 do
          iter_raw_backtrace_slot f (get_raw_backtrace_slot bt i)
        done
    val exn_slot_id : exn -> intPrintexc.exn_slot_id returns an integer which uniquely identifies
    the constructor used to create the exception value exn
    (in the current runtime).
val exn_slot_name : exn -> stringPrintexc.exn_slot_name exn returns the internal name of the constructor
    used to create the exception value exn.