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Re: Let's get lazy

by japhy (Canon)
on Aug 28, 2001 at 20:47 UTC ( #108500=note: print w/replies, xml ) Need Help??

in reply to Let's get lazy

I'd suggest creating a function (or an object) that returns the next term in your requested series. The secret to laziness is an iterator.
{ my $init = 'aa'; my $start = 'a'; my $len = length $init; sub next_term { my $ret = $init; my $p = $len - 1; while (1) { substr($init, $p, 1) =~ tr/acgnt/cgnta/; last if substr($init, $p--, 1) ne $start; $init = "$start$init", $len++, last if $p < 0; } return $ret; } }
You could also mimic this with a tied scalar, and have the FETCH function do what I have done above.
package Tie::ScalarIter; sub TIESCALAR { my ($class, $init, $start) = @_; bless [ $init, $start, length($init) ], $class; } sub FETCH { my $s = shift; my $ret = $s->[0]; my $p = $s->[2] - 1; while (1) { substr($s->[0], $p, 1) =~ tr/acgnt/cgnta/; last if substr($s->[0], $p--, 1) ne $s->[1]; $s->[0] = "$s->[1]$s->[0]", $s->[2]++, last if $p < 0; } return $ret; } sub STORE { my $s = shift; my $rep = shift; if (ref $rep) { @$s = (@$rep, length $rep->[0]) } else { (@$s[0,2] = ($rep, length $rep) } } 1;
Both interfaces are simple to use:
# functional my @strings; while (defined (my $next = next_term())) { last if length($next) > 4; push @strings, $next; } # tied scalar use Tie::ScalarIter; tie my($iter), 'Tie::ScalarIter', 'aa', 'a'; my @strings; while (defined (my $next = $iter)) { last if length($next) > 4; push @strings, $next; }
And that's about it.

Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

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