my ($alpha, $beta);
$alpha = $beta = << "EOF";
    my $self = shift;
    ...
    foreach ...
        if ...
            if ...
                if ...
                    push @foo, [ @bar ];
                }
            }
        } else {
            push @foo, [ @bar ];
        }
    }
    push @foo, [ @bar ];
    return \@foo;
END
$beta =~ s/(push \@foo, \[ \@bar \]);/$1 if \$self->\{baz\} eq \$gamma;/gs;
$beta =~ s/sub alpha/sub beta/;

sub alpha {
  eval $alpha;
}
sub beta {
  eval $beta;
EOF