`Interpolation.pm`

The syntax actually looks like this:

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

        $PROFITS = ($earnings - $expenses)/100;  
        $state = "maryland";
        $s = "$${$PROFITS} in the state of $Cap{$state}";

                $104,254.12 in the state of Maryland

        $data = 'Cleveland, "Ohio"';
        $t .= qq{The data are: $q{$data}.};

                The data are: "Cleveland, \"Ohio\""

        $text = "x --> y";
        print qq{<a href="move.cgi?x,y">$HTML{$text}</a>};

                # .... x --&gt; y ....

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.