use strict;
use warnings;
use feature 'say';
BEGIN {
        package My::Types;
        use Type::Library 1.012
                -utils,
                -extends => [ 'Types::Standard' ],
                -declare => 'JSONCapable';
         
        declare JSONCapable,
                as Undef
                |  ScalarRef[ Enum[ 0..1 ] ]
                |  Num
                |  Str
                |  ArrayRef[ JSONCapable ]
                |  HashRef[ JSONCapable ]
                ;
}
use My::Types 'is_JSONCapable';
my $var = {
        foo => 1,
        bar => [ \0, "baz", [] ],
};
say is_JSONCapable $var;