Perl6 optional types

gistfile1.md

sub test(Int $a) { say $a + 3 }
test(23); # 26

sub test(Int $a) { say $a + 3 }
test("23"); # Calling 'test' will never work with argument types (str) (line 1)
            #    Expected: :(Int $a)

sub test(Int $a) { say $a + 3 }
my $b = "23";
test($b); # runtime error: Nominal type check failed for parameter '$a'; expected Int but got Str instead

sub test($a) { say $a + 3 }
test("23"); # 26

sub test(Int $a) { say $a + 3 }
my $b = "23";
test($b); # 26