All good points. Here is a little Benchmark that makes your point:

use Benchmark;

$iterations = 1000000;     

$name1 = "Alternation"; 
$code1 = ' $_="ABBA"; s/(A|B)/X/g; ';

$name2 = "Class"; 
$code2 = ' $_="ABBA"; s/[AB]/X/g; ';

$name3 = "Substitution"; 
$code3 = ' $_="ABBA"; s/A/X/g; ';

$name4 = "Transliterate"; 
$code4 = ' $_="ABBA"; tr/A/X/; ';

timethese($iterations, {$name1 => $code1, 
                        $name2 => $code2,
                        $name3 => $code3,
                        $name4 => $code4,
                        } );

__END__

C:\>perl test.pl

Benchmark: timing 1000000 iterations of Alternation, Class, Substituti
+on, Transliterate...

Alternation:   36 wallclock secs (35.92 usr +  0.00 sys = 35.92 CPU) @
+ 27839.64/s  (n=1000000)
     Class:    23 wallclock secs (23.12 usr +  0.00 sys = 23.12 CPU) @
+ 43252.60/s  (n=1000000)
Substitution:  20 wallclock secs (20.81 usr +  0.00 sys = 20.81 CPU) @
+ 48053.82/s  (n=1000000)
Transliterate:  8 wallclock secs ( 8.07 usr +  0.00 sys =  8.07 CPU) @
+ 123915.74/s (n=1000000)

C:\>
[download]

But if we are going to get into a little recreational optimisation.....

# mine.pl

sub show {
    my @data = @_;
    for (@data) {
        s/\266/%B6/g;
        s/\267/%B7/g;
        tr/ /\267/;
        s/\t/ -> /g;
        s/\n/\266\n/g;
    }
  return wantarray ? @data : join'',@data;
}

@data = (<DATA>)[0..7];
my $start = time;
for (0..100000) { my @new = show(@data) }
printf "Mine takes %d seconds", (time - $start);

__DATA__
    tab
    4 spaces, trailing tab    
        tab and 4 spaces
        
 -> tab¶
····4·spaces,·trailing·tab -> ¶
 -> ····tab·and·4·spaces¶
 ->  -> ¶
¶


# yours.pl

my %mapping = (
    "\t"   => ' -> ',
    " "    => chr(0267),
    "\n"   => chr(0266)."\n",
    "\266" => '%B6',
    "\267" => '%B7',
    );

my $pattern = qr/([@{[join '', keys %mapping]}])/;

sub show {
    my @data = @_;
    s/$pattern/$mapping{$1}/g for (@data);
    return wantarray ? @data : join'',@data;
}

@data = (<DATA>)[0..7];
my $start = time;
for (0..100000) { my $new = show(@data) }
printf "Yours takes %d seconds", (time - $start);

__DATA__
    tab
    4 spaces, trailing tab    
        tab and 4 spaces
        
 -> tab¶
····4·spaces,·trailing·tab -> ¶
 -> ····tab·and·4·spaces¶
 ->  -> ¶
¶
[download]

You can't use Benchmark fairly on yours as the hash set up is a once only so I just use time and run a loop on the respective subs. If you run this code you will notice that my code takes half as long as yours as there is no hash look up involved. Had to salvage a little face :-)

TIMTOWTDI!

C:\>perl mine.pl
Mine takes 59 seconds
C:\>perl yours.pl
Yours takes 119 seconds
C:\>

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print