use 5.012;
use warnings;

sub catsub {
  my @fs = @_;
  sub { map { $_->(@_) } @fs }
}

my %test = (
    code => sub {
        my $input = shift;
        say '[original]';
        if ($input eq 'h') { return 'hallo'; }
    },
);

$test{code} = catsub(
    $test{code},
    sub {
        my $input = shift;
        say '[erweiterung]';
        if ($input eq 's') { return 'sonne'; }
    },
    sub {
        say '[nix]';
        ();
    },
);

say $test{code}->('h');
say $test{code}->('s');