...prog....(main)....(statements in package main here)..
use strict;
use Readonly;
...then a package definition in middle of prog....
package my_temp_convert;
our $VERSION = '.01';
require Exporter;
our @ISA = ('Exporter');
our @EXPORT = qw(set_temp, set_scale, c, f);
my curr_scale=0; #centigrade, 1=faren
my cur_ctemp=0;
sub set_scale{ curr_scale=shift}
sub set_temp($){#convert to C if needed, and store in "curtmp"}
sub c {return cur_temp;}
sub f {return 32+(9*cur_temp)/5}
#now back to main....

package main;

# somehow "use the above, inline package, "temp_convert";

set_scale(1);
set_temp(32);

print "%d F is %d C\n", f(), c();  #prints "32 F is 0 C" 
#end prog