How can I check if a parameter is a subroutine?

How can I test if a given parameter is a subroutine?

For example:

sub foo {
    my $bar = shift;
    if (is_subroutine($bar)) {
        return &$bar();
    }
    return 0;
}

I’d call this like:

foo(sub { print "Hi!" }); # prints "Hi!"
foo(123); # Nothing

How can I do this?

>Solution :

You can try to dereference the scalar as a subroutine with &{...} and then check if the result exists.

if (exists &{$bar}) {
  ...
}

Also, $bar() is not valid syntax for calling a subroutine stored in a scalar reference. You’ll need to write either &{$bar}() or $bar->() (the latter is sugar for the former)