Since the original intent appeared to be to run just one subroutine, you can probably even lose the subroutine in chromatics example:

my $in = param('in');

my %actions = (
    this => \&this,
    that => \&that,
    foo => \&foo,
    bar => \&bar,
    zzz => \&sleepytime,
);

defined(my $sub_ref = $actions{$in}) &&  $sub_ref->() ;
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-mark