Perl 6 and Parrot Essentials, 2nd Edition

Subroutine Stubs

To declare a subroutine without defining it you give it a body consisting of nothing but the . . . (or “yada, yada, yada”) operator. So, all the preceding examples that look like pseudocode with { . . . } for their body are actually valid subroutine declarations.

sub stubbly (Str $name, Int ?$days) { . . . }

When you later define the subroutine, the signature and defined traits must exactly match the declaration.

sub stubbly (Str $name, Int ?$days) {
    print "$name hasn't shaved in $days day";
    print "s" if $days > 1;
}