use 5.010;

my $x = 40;

given ($x)
{
	when ([0..9,   50..59])   { say 0 }
	when ([10..19, 60..69])   { say 1 }
	when ([20..29, 70..79])   { say 2 }
	when ([30..39, 80..89])   { say 3 }
	when ([40..49, 90..99])   { say 4 }
}

##</code><code>##

use 5.014;

my $x = 40;

given ($x)
{
	say 0 when [0..9,   50..59];
	say 1 when [10..19, 60..69];
	say 2 when [20..29, 70..79];
	say 3 when [30..39, 80..89];
	say 4 when [40..49, 90..99];
}

##</code><code>##

use 5.010;

my $x = 40;

say 0 if $x ~~ [0..9,   50..59];
say 1 if $x ~~ [10..19, 60..69];
say 2 if $x ~~ [20..29, 70..79];
say 3 if $x ~~ [30..39, 80..89];
say 4 if $x ~~ [40..49, 90..99];

##</code><code>##

use Smart::Dispatch;

my $x = 40;

my $tiers = dispatcher {
	match [0..9,   50..59], dispatch { 0 };
	match [10..19, 60..69], dispatch { 1 };
	match [20..29, 70..79], dispatch { 2 };
	match [30..39, 80..89], dispatch { 3 };
	match [40..49, 90..99], dispatch { 4 };
};

say $tiers->($x);

##</code><code>##

my $x = 40;

my %tiers = (
 (map { $_ => 0 }  0..9,   50..59),
 (map { $_ => 1 }  10..19, 60..69),
 (map { $_ => 2 }  20..29, 70..79),
 (map { $_ => 3 }  30..39, 80..89),
 (map { $_ => 4 }  40..49, 90..99),
);

print $tiers{$x} . "\n";

##</code><code>##

use 5.010;

my $standard_say = sub {
  say 0 if $x ~~ [0..9,   50..59];
  say 1 if $x ~~ [10..19, 60..69];
  say 2 if $x ~~ [20..29, 70..79];
  say 3 if $x ~~ [30..39, 80..89];
  say 4 if $x ~~ [40..49, 90..99];
};

$standard_say->(40);

# Now imagine we decide to special-case 39...
my $modified_say = sub {
  if ($_[0] == 39) {
    say "yay!";
    return;
  }
  $standard_say->(@_);
};

$modified_say->(40);
$modified_say->(39);

##</code><code>##

use Smart::Dispatch;

my $standard_say = dispatcher {
	match [0..9,   50..59], dispatch { say 0 };
	match [10..19, 60..69], dispatch { say 1 };
	match [20..29, 70..79], dispatch { say 2 };
	match [30..39, 80..89], dispatch { say 3 };
	match [40..49, 90..99], dispatch { say 4 };
};

$standard_say->(40);

my $modified_say = dispatcher { match 39, dispatch { say "yay!" } } . $standard_say;

$modified_say->(40);
$modified_say->(39);