module Printexc: sig .. end
Facilities for printing exceptions and inspecting current call stack.
val to_string : exn -> string
Printexc.to_string e returns a string representation of
val print : ('a -> 'b) -> 'a -> 'b
Printexc.print fn x applies
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 -> 'b
Printexc.catch fn x
is similar to
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
does. Moreover, calling
makes it harder to track the location of the exception
using the debugger or the stack backtrace facility.
So, do not use
in new code.
val print_backtrace : Pervasives.out_channel -> unit
Printexc.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.
val get_backtrace : unit -> string
Printexc.get_backtrace () returns a string containing the
same exception backtrace that
val record_backtrace : bool -> unit
Printexc.record_backtrace b turns recording of exception backtraces
b = true) or off (if
b = false). Initially, backtraces
are not recorded, unless the
b flag is given to the program
val backtrace_status : unit -> bool
true if exception
backtraces are currently recorded,
false if not.
val register_printer : (exn -> string option) -> unit
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
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
Some s value (if no such printer exists, the runtime will use a
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.
The abstract type
backtrace stores exception backtraces in
a low-level format, instead of directly exposing them as string as
get_backtrace() function does.
This allows to pay the performance overhead of representation
conversion and formatting only at printing time, which is useful
if you want to record more backtrace than you actually print.
Current call stack
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