*marvell has asked for the wisdom of the Perl Monks concerning the following question:*

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

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