Printexc

# Module Printexc

    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 the exception `e`.

    val print : ('a -> 'b) -> 'a -> 'b

`Printexc.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 -> 'b

`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.

    val print_backtrace : 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.
Since 3.11.0

    val get_backtrace : unit -> string

`Printexc.get_backtrace ()` returns a string containing the same exception backtrace that `Printexc.print_backtrace` would print.
Since 3.11.0

    val record_backtrace : bool -> unit

`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.
Since 3.11.0

    val backtrace_status : unit -> bool

`Printexc.backtrace_status()` returns `true` if exception backtraces are currently recorded, `false` if not.
Since 3.11.0

    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 `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).

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.
Since 3.11.2

###### Raw backtraces

    type raw_backtrace

The abstract type `backtrace` stores exception backtraces in a low-level format, instead of directly exposing them as string as the `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.

    val get_raw_backtrace : unit -> raw_backtrace

    val print_raw_backtrace : out_channel -> raw_backtrace -> unit

    val raw_backtrace_to_string : raw_backtrace -> string

###### Current call stack

    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.)