use warnings;
use strict;


BEGIN {  # closure: data in scope only to create_f() function

my $common = 'fooble';

sub create_f {

    my ($user_source,  # required: string: user source code
        ) = @_;

    my $private = 'xpto';

    # ??? makes $common variable defined in eval ???
    # any of these statements do the trick.
    # except as noted, tested in both 5.6.1 and 5.8.2
    # print "in create_f(): common: $common \n";
    # $common .= '';
    map defined, $common;  # note: not tested with 5.6.1

    my $coderef = eval qq{ sub { $user_source } };

    return $coderef;  # code reference undefined if eval failed

    }

}  # end closure: create_f() function


# NOTE: single quotes on here-doc tag below: no interpolation.
my $function = create_f(<<'USER_CODE');
    my $param = shift;
    print "param: $param   common: $common   private: $private \n";
    return join ';', $param, $common, $private;
USER_CODE

my $freturn = $function->('hi there');
print "function return: `$freturn' \n";

##</code><code>##

>perl t_create_f_PM.pl
param: hi there   common: fooble   private: xpto
function return: `hi there;fooble;xpto'

##</code><code>##

>perl t_create_f_PM.pl
Use of uninitialized value in concatenation (.) or string at (eval 1) line 2.
param: hi there   common:    private: xpto
Use of uninitialized value in join or string at (eval 1) line 3.
function return: `hi there;;xpto'