BatPrintexc
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 -> unit
print_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 -> unit
Print an exception. The stdlib print
function is now named !pass
.
val raise_with_backtrace : exn -> Printexc.raw_backtrace -> 'a
Reraise the exception using the given raw_backtrace for the origin of the exception
type raw_backtrace = Printexc.raw_backtrace
The 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_backtrace
Printexc.get_raw_backtrace ()
returns the same exception backtrace that Printexc.print_backtrace
would print, but in a raw format.
val print_raw_backtrace : out_channel -> raw_backtrace -> unit
Print a raw backtrace in the same format Printexc.print_backtrace
uses.
val raw_backtrace_to_string : raw_backtrace -> string
Return a string from a raw backtrace, in the same format Printexc.get_backtrace
uses.
val get_callstack : int -> raw_backtrace
Printexc.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 -> unit
Printexc.default_uncaught_exception_handler
prints the exception and backtrace on standard error output.
val set_uncaught_exception_handler : (exn -> raw_backtrace -> unit) -> unit
Printexc.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_slot
The abstract type backtrace_slot
represents a single slot of a backtrace.
val backtrace_slots : raw_backtrace -> backtrace_slot array option
Returns 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
)type location = Printexc.location = {
filename : string; |
line_number : int; |
start_char : int; |
end_char : int; |
}
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 raw_backtrace_slot = Printexc.raw_backtrace_slot
This 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 -> int
raw_backtrace_length bckt
returns the number of slots in the backtrace bckt
.
val get_raw_backtrace_slot : raw_backtrace -> int -> raw_backtrace_slot
get_raw_backtrace_slot bckt pos
returns the slot in position pos
in the backtrace bckt
.
val convert_raw_backtrace_slot : raw_backtrace_slot -> backtrace_slot
Extracts the user-friendly backtrace_slot
from a low-level raw_backtrace_slot
.
val get_raw_backtrace_next_slot : raw_backtrace_slot -> raw_backtrace_slot option
get_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).
Printexc.exn_slot_name exn
returns the internal name of the constructor used to create the exception value exn
.
Printexc.use_printers e
returns None
if there are no registered printers and Some s
with else as the resulting string otherwise.
Printexc.to_string_default e
returns a string representation of the exception e
, ignoring all registered exception printers.
type raw_backtrace_entry = Printexc.raw_backtrace_entry
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_slot
s. 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_slot
s. However, if two raw_backtrace_entry
s are equal as integers, then they represent the same backtrace_slot
s.
val raw_backtrace_entries : raw_backtrace -> raw_backtrace_entry array
val backtrace_slots_of_raw_entry : raw_backtrace_entry -> backtrace_slot array option
Returns 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.