Let us create a program that tries to open a nonexisting file and read the first line from it:

my $f = open 'dummy.txt';
say $f.get;

This program will raise an exception:

Failed to open file /Users/ash/code/exceptions/dummy.txt: no such file or directory
  in block <unit> at 14.pl line 1

Notice that the exception happens only after an attempt to read from a file happens. Simply opening a file does not create an error, it only sets the $f file handler to the Failure object.

The failure object is a wrapper around an Exception object. The exception itself is reachable via the exception method:

my $f = open 'dummy.txt';
say $f.exception;

It prints the error message:

Failed to open file /Users/ash/code/exceptions/dummy.txt: no such file or directory

You can test a failure object in the Boolean context, for example, immediately after opening...