<a b c>.map: *.uc;     # same as <a b c>.map: -> $char { $char.uc } 

##</code><code>##

 Str $file where *.IO.f = 'file.dat',

##</code><code>##

Str $file where -> $x {$x.IO.f} = 'file.dat',

##</code><code>##

#b.raku

sub MAIN(
  Str $file where -> $x {$x.IO.f} = 'a.txt',
  Int  :$length = 24,
  Bool :$verbose
) {
    say $length if $length.defined;
    say $file   if $file.defined;
    say 'Verbosity ', ($verbose ?? 'on' !! 'off');
}

--output:--
$ raku b.raku
24
a.txt
Verbosity off


$ raku b.raku --verbose --length=7 a.raku
7
a.raku
Verbosity on