contribute-now-argfiles.txt

This Week's Contribution to Perl 6 Week 8: Implement $*ARGFILES for Rakudo
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<p>For this week's contribution to Perl 6 we ask you to implement the
<code>$*ARGFILES</code> special variable (and underlying object) for
Rakudo.</p>

<p>(<a
    href="http://perlgeek.de/blog-en/perl-6/contribute-now-announce.html">Introduction
    to this series of challenges</a>)</p>

<h2>Background</h2>

<p>In Perl 5, there is a "magic" way to iterate over input: <code>while (my
$line = &lt;&gt;) { ... }</code>. This reads from standard input if no command
line arguments were provided. If there are command line arguments, they are
taken as file names, and <code>&lt;&gt;</code> iterates over the contents of
these files.</p>

<p>In Perl 6 this magic is performed with the <code>$*ARGFILES</code> special
variable. Please implement it!</p>

<p>To do that, you have to understand how file reading works in Perl 6. Once
you have a file handle, there are two ways to read lines: either by calling
<code>$handle.get</code>, which returns just one line, or by calling
<code>$handle.lines</code>, which returns a (lazy) list of all the remaining
lines.</p>

<p>You can obtain the command line arguments from <code>@*ARGS</code>, open a
file with <code>my $handle = open $filename;</code> for reading; And finally
you can use <code>lines('filename')</code> to read all lines from a file.</p>


<h2>What you can do</h2>

<p>Implement a backend class for <code>$*ARGFILES</code>. You can do that in
normal Perl 6 code, no need to change the actual compiler. Once that's done,
we will plug it into Rakudo. Your code might look like this:</p>

<pre>[%syntax perl6 %]
class IO::ArgFiles {
    has @!filenames;
    method get() { ... }
    method lines() { ... }
    method filename() {
        # return the current filename, or '-' if standard input
        ...
    }
}
my $*ARGFILES = IO::ArgFiles.new(filenames => @*ARGS);
.say for $*ARGFILES.lines();
[% endsyntax %]</pre>

<p>(Of course this is only a rough skeleton, you might need to change some
details, or add some things).</p>

<h2>Submission</h2>

<p>Please submit your source code to the <a
href="mailto:perl6-compiler@perl.org">perl6-compiler@perl.org</a> mailing
list (and put moritz.lenz@gmail.com on CC,
because the mailing list sometimes lack quite a bit).</p>

<p><strong>Update:</strong>: there have been two submissions, and a mixture of
both has been applied.</p>

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