use v5.12;
use warnings;
use Sort::Key qw/ikeysort/;
use Data::Dump qw/pp dd/;

my $n;
my %order = map {$_ => ++$n}
  qw/monday tuesday wednesday thursday friday saturday sunday/;


pp ikeysort { $order{lc($_)} } qw/Monday Saturday Thursday/;

##</code><code>##

("Monday", "Thursday", "Saturday")