#!/usr/bin/perl -w
use v5.20;
use re 'strict';

$_ = 'my$a=5;';
my $re = qr/
    (?<statements>(?&statement)*)
    (?(DEFINE)
      (?<statement> my \$ (?&identifier) = \d ; )
      (?<identifier> [a-z] )
    )/x;
$_ =~ $re;
say $+{statements};
# Assuming I do the $^R and $^N stuff to create a parse tree, then it would be nice, if I could write something like:
# ${$r->{statements}[0]->{identifier}} = 'b';
# in order to change $_ to "my$b=5;"
# similar in spirit to substring references:
# my $s = \substr $_, 3, 1;
# $$s = 'b';