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Tue, 29 Jun 2010

This Week's Contribution to Perl 6 Week 8: Implement $*ARGFILES for Rakudo


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For this week's contribution to Perl 6 we ask you to implement the $*ARGFILES special variable (and underlying object) for Rakudo.

(Introduction to this series of challenges)

Background

In Perl 5, there is a "magic" way to iterate over input: while (my $line = <>) { ... }. 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 <> iterates over the contents of these files.

In Perl 6 this magic is performed with the $*ARGFILES special variable. Please implement it!

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 $handle.get, which returns just one line, or by calling $handle.lines, which returns a (lazy) list of all the remaining lines.

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

What you can do

Implement a backend class for $*ARGFILES. 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:

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();

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

Submission

Please submit your source code to the perl6-compiler@perl.org mailing list (and put moritz@faui2k3.org on CC, because the mailing list sometimes lack quite a bit).

Update:: there have been two submissions, and a mixture of both has been applied.

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