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    <p>Functional Programming* to the rescue! The following code won't be too efficient, but far cleaner.</p> <p>We will define a function that takes a number and a list as arguments. The number denotes how many times we have to recurse, the list holds the letters from the outer levels.</p> <pre><code>#!/usr/bin/perl use strict; use warnings; my @list = 'a' .. 'z'; # lowercase letters sub combinations { my ($recursions, @letters) = @_; # unpack the arguments if ($recursions == 0) { print @letters, "\n"; # print the letters, append newline } else { # do a loop $recursions--; # reduce level for my $letter (@list) { combinations($recursions, @letters, $letter); } } } </code></pre> <p>We can call that sub with <code>combinations(8);</code> to get the expected result.</p> <p>The <code>..</code> is the range operator and produces a list. It works with alphabetic characters too. You will want <code>'a' .. 'z', 0 .. 9</code>.</p> <p>It works, although you might want to use a smaller <code>@list</code> for testing.</p> <p>This produces all fixed-length strings. To get all strings <em>up to</em> a given length, just do</p> <pre><code>combinations($length) foreach my $length (1 .. 8); </code></pre> <p>(breadth-first), or include </p> <pre><code>print @list, "\n"; </code></pre> <p>just before the <code>for</code>-loop in the <code>else</code>-branch for depth-first.</p> <p>Footnotes:</p> <p>(*) No, not really, but this is something close. Functional Programming does not require <em>any</em> loops at all.</p>
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    1. COHi, thanks so much for your help! I'm getting a Global symbol "$length" requires explicit package name error when I try to put the loop in? Am I missing something obvious?
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    2. COAh, sorry, I forgot a `my` there — fixed :-)
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