switch ( $foo ) {
    case ( tr/I/I/ == 1 ) { $bar = 'low' }
    case ( tr/I/I/ == 2 ) { $bar = 'med' }
    case ( tr/I/I/ == 3 ) { $bar = 'high' }
    else { warn "Bad $_\n" }
}
[download]

Use of uninitialized value $_ in transliteration (tr///)
[download]

(Update: Because switch doesn't set $_, it filters the source code - in this case "insanely".)

#!perl! -w
use strict;
use Switch;

my $foo = 'II';
print $foo =~ tr/I/I/, "\n";
my $bar;
switch ( $foo ) {
    case ( tr/I/I/ == 1 ) { $bar = 'low' }
    case ( tr/I/I/ == 2 ) { $bar = 'med' }
    case ( tr/I/I/ == 3 ) { $bar = 'high' }
    else { $bar = "drat" }
}

print "Foo: $foo Bar: $bar\n";

# This works:
switch ( $foo ) {
    case ( /I{3}/ ) { $bar = 'high' }
    case ( /I{2}/ ) { $bar = 'med' }
    case ( /I/ )    { $bar = 'low' }
    else { $bar = "drat" }
}

print "Foo: $foo Bar: $bar\n";
[download]

Update: Thanks kyle and jeffa, the lesson is learned - don't use Switch. (jeffa's solution indeed doesn't work - which surprised me)

Update2: moritz has it right, use the (5.010) given-when construct:

given ( $foo ) {
    when ( tr/I/I/ == 1 ) { $bar = 'low' }
    when ( tr/I/I/ == 2 ) { $bar = 'med' }
    when ( tr/I/I/ == 3 ) { $bar = 'high' }
    default { $bar = "drat" }
}
[download]