IO::Lambda::Backtrace - backtrace chains of events


The module makes it easier to debug chains of events, when a lambda awaits for another, this one in turn for another, etc etc. The class IO::Lambda::Backtrace represents a set of such stacks, because a lambda can be awaited by more than one lambda. Each stack is an array of items where each contains the caller lambda and the invocation point. The class provides helper methods for printing this information in readable form.

The module relies on the debug information about invocation points collected by IO::Lambda. By default, there's very little information collected, so in order to increase verbosity use IO::Lambda::DEBUG_CALLER flag, either directly or through $ENV{IO_LAMBDA_DEBUG} = 'caller'. If the flag is set to 1, lambdas collect invocation points. If the flag is set to 2, then also the additional perl stack trace is added.


  use IO::Lambda;
  $IO::Lambda::DEBUG_CALLER = 1;

  lambda {
     warn this-> backtrace-> as_text;

or from command line

   env IO_LAMBDA_DEBUG=caller=2 ./myscript



Extracts the information of the current chain of events and creates a new blessed reference of it.


Returns the backtrace information formatted as text, ready to display


Warns with the backtrace log


Dies with the backtrace log


Dmitry Karasik, <>.

The ideas of backtracing threads of events, and implementing backtrace objects passable through execition stack are proposed by Ben Tilly.