# InferWhatever.pm                                          20oct08waw


package InferWhatever; {  # begin package closure

use warnings;
use strict;

our $VERSION = '0.1.0';

our @EXPORT    = ();
our @EXPORT_OK = qw(series);

use Exporter;
our @ISA = qw(Exporter);


sub Iterator (&) { return $_[0] }

sub series {

    return if @_ < 2;

    my @s = @_;

    # at least 2 parameters: 1st difference(s) must exist.
    my @d1 = map $s[$_] - $s[$_-1], 1 .. $#s;

    # repeat sequence: 3, 3, ...
    return Iterator { return $s[-1] } if zeros(@d1);

    # any 2nd difference(s) (at least 3 parameters)?
    return unless my @d2 = map $d1[$_] - $d1[$_-1], 1 .. $#d1;

    # arithmetic sequence: 5, 9, 13, ...
    return Iterator { return $s[-1] += $d1[-1] } if zeros(@d2);

    # any 3rd difference(s) (at least 4 parameters)?
    return unless my @d3 = map $d2[$_] - $d2[$_-1], 1 .. $#d2;

    # quadratic sequence: 1, 4, 9, 16, ...
    return Iterator { $s[-1] += $d1[-1] += $d2[-1] } if zeros(@d3);

    return;  # that's all for now ########################

    # any 4th difference(s) (at least 5 parameters)?
    return unless my @d4 = map $d3[$_] - $d3[$_-1], 1 .. $#d3;

    }


sub zeros { return unless @_;  $_ and return for @_;  return 1 }


}  # end package InferWhatever closure


1;  # inclusion success