How do I test a dynamic variable for existence?

As I understand, Dynamic Variables are looked up at runtime. I want to use them to enable parametrization similar to racket parameters.

To do so, I have to set a default that should be overridable, but not necessarily changable. My current approach is fairly simplistic:

my $*param ::= 42;
sub parameterized-function { say $*param };
parameterized-function();
do {
    my $*param ::= 15;
    parameterized-function();
}

Which works just fine - except that it introduces the name of the parameter on the outer scope. Beyond just feeling untidy, this has the side-effect that my $*param = 15; causes mayhem if used on the file level.

What I would like to do instead is check if the parameter has been defined on the call stack, along the lines of:

sub parameterized-function { if defined($*param) { say 42 } else { say $*param } };

So, is it possible to perform such a check, if so how is it done?

Quoting S02:

User-defined dynamic variables should generally be initialized with ::= unless it is necessary for [the] variable to be modified. (Marking dynamic variables as readonly is very helpful in terms of sharing the same value among competing threads, since a readonly variable need not be locked.)

If you want to access a dynamic variable that has not been defined in the current (dynamic) scope, either of the following should work:

$*param // 'default value'

# Any if not found
DYNAMIC::<$*param>

# Nil if not found
try $*param

# Mu if not found
use nqp;
nqp::getlexdyn('$*param')

As I have not looked into what you're trying to accomplish, there might be more appropriate solutions.