infinite series

[marvell]

As an excersise in learning "tie", I knocked up this series generator. I know this is probably not the ideal solution to the problem of generating series, but it was "tie" I was interested in.

I would very much apreciate your comments on my implementation.

Series.pm

package Series;

use strict;

sub TIEARRAY {

    my $pkg = shift;

    my $rsub = shift; # sub for formula

    my @vals = @_;

    bless { 'values' => [ @vals ],
            'next' => $rsub
            }, $pkg;

}

sub FETCHSIZE {

    # rather meaningless in context, but gets called a lot
    # presume it's to check that any values at all exist

    return 1; # for now
}

sub FETCH {

    die "can't get subscripted value of series";

}

sub SHIFT {

    my ($obj) = @_;

    my $ra = $obj->{'values'};

    push(@$ra, $obj->{'next'}->(@$ra));

    return shift @$ra;
}

1;

series.pl

#!/usr/bin/perl -w 

use strict;
use Series;

print "Arithmetic Series: 1,4,7, ... N_{i-1}+3 ...\n";

tie my @arith, 'Series', sub { return 3 + shift }, 1;

print shift(@arith)." " for (1..15);
print "\n\n";

print "Geometric Series: 1,2,4, ... N_{i-1}*2 ...\n";

tie my @geo, 'Series', sub { return 2 * shift }, 1;

print shift(@geo)." " for (1..15);
print "\n\n";

print "Combination Series: 2,7,17, ... N_{i-1}*2+3 ...\n";

tie my @combo, 'Series', sub { return 3 + 2 * shift }, 2;

print shift(@combo)." " for (1..15);
print "\n\n";

print "Fibonacci Numbers: 0,1,1,2,3, ... N_{i-1}+N_{i-2} ...\n";

tie my @fibo, 'Series', sub { my @n = @_; return $n[0]+$n[1] }, 0,1;

print shift(@fibo)." " for (1..15);
print "\n";

And here is the output:

Arithmetic Series: 1,4,7, ... N_{i-1}+3 ...
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 

Geometric Series: 1,2,4, ... N_{i-1}*2 ...
1 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 

Combination Series: 2,7,17, ... N_{i-1}*2+3 ...
2 7 17 37 77 157 317 637 1277 2557 5117 10237 20477 40957 81917 

Fibonacci Numbers: 0,1,1,2,3, ... N_{i-1}+N_{i-2} ...
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

--
Brother Marvell

Edit: chipmunk 2001-05-16