use strict;
use warnings;
use feature 'say';
no autovivification;
use Data::Dump qw/pp/;


sub sub_exists{
  my $name = shift;

  return
    exists $::{$name}           # symbol exists
    &&
    (
     ref $::{$name} eq "CODE"   # only code
     ||
     (*{$::{$name}}{CODE} && 1) # also code
     ||
     !1                         # false
    );

}


for my $name (qw/zero one two three/) {
  pp { $name => sub_exists($name) };
}


our $one=1;

our $two=2;
sub two {2};

sub three {3}


  

##</code><code>##

{ zero => "" }
{ one => "" }
{ two => 1 }
{ three => 1 }