`Interpolation.pm`

The syntax actually looks like this:

        use Interpolation '$' => \&currency,
                          'q' => \&quote_for_CSV,
                          'Cap' => sub { ucfirst lc  $_[0] };

        $s = "$${$PROFITS} in the state of $Cap{$state}";
        $t .= qq{The data are: "$q{$data}".};

Prevents cluttering of code with lost of calls to formatting functions
Attention focused on output rather than on formatting code
Define formatters with mnemonic names like $currency or $Cap.
Clever hack:

        use Interpolation 's' => 'sprintf1';

        print "Profits were up by $s{'%2.2f',$amt} percent.\n";

Inserts sprintf call into a quoted string.