This has already been done by the regex ninja japhy in the funky YAPE::Regex::Explain module.

use YAPE::Explain::Regex;

my $re = qr/foo*(?<=bar)+?(?:baz)?/;
print YAPE::Regex::Explain->new($re)->explain;

__output__

The regular expression:

(?-imsx:foo*(?<=bar)(?:baz)?)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  fo                       'fo'
----------------------------------------------------------------------
  o*                       'o' (0 or more times (matching the most
                           amount possible))
----------------------------------------------------------------------
  (?<=                     look behind to see if there is (1 or more
                           times (matching the least amount
                           possible)):
----------------------------------------------------------------------
    bar                      'bar'
----------------------------------------------------------------------
  )+?                      end of look-behind
----------------------------------------------------------------------
  (?:                      group, but do not capture (optional
                           (matching the most amount possible)):
----------------------------------------------------------------------
    baz                      'baz'
----------------------------------------------------------------------
  )?                       end of grouping
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
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HTH

_________
broquaint