Facilities for printing exceptions.
Printexc.pass 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. This function is a renamed version of Printexc.print from stdlib.
Printexc.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.
Printexc.to_string e returns a string representation of the exception e.
val print_backtrace : _ BatInnerIO.output -> unitprint_backtrace oc Prints the 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.
Printexc.get_backtrace () returns a string containing the same exception backtrace that Printexc.print_backtrace would print.
Printexc.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.
Printexc.backtrace_status() returns true if exception backtraces are currently recorded, false if not.
Printexc.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
s with s 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).
val print : _ BatInnerIO.output -> exn -> unitPrint an exception. The stdlib print function is now named !pass.
type raw_backtrace = Printexc.raw_backtraceThe abstract type raw_backtrace stores a backtrace in a low-level format, instead of directly exposing them as string as the get_backtrace() function does.
This allows delaying the formatting of backtraces to when they are actually printed, which may be useful if you record more backtraces than you print.
Raw backtraces cannot be marshalled. If you need marshalling, you should use the array returned by the backtrace_slots function of the next section.
val 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.
val print_raw_backtrace : Pervasives.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 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 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 prints the exception and backtrace on standard error output.
Note that when fn is called all the functions registered with Pervasives.at_exit have already been called. Because of this you must make sure any output channel fn writes on is flushed.
If fn raises an exception, it is ignored.
Those function allow to traverse the slots of a raw backtrace, extract information from them in a programmer-friendly format.
type backtrace_slot = Printexc.backtrace_slotThe 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)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 ... endtype raw_backtrace_slot = Printexc.raw_backtrace_slotThis type allows direct access to raw backtrace slots, without any conversion in an OCaml-usable data-structure. Being process-specific, they 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_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.
Printexc.exn_slot_id returns an integer which uniquely identifies the constructor used to create the exception value exn (in the current runtime).