There is nothing like a missing argument with signatures: 
#!/usr/bin/perl
use warnings;
use strict;

use experimental 'signatures';
use Syntax::Construct qw{ // };

sub show ($arg) { $arg // 'undef' }

use Test::More;
use Test::Exception;

throws_ok { show() } qr/Too few arguments/;

done_testing();

[download]
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Distinguish between missing and undefined arguments with subroutine signatures by choroba
in thread Distinguish between missing and undefined arguments with subroutine signatures by jo37

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