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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)


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 = => @*ARGS);
.say for $*ARGFILES.lines();

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


Please submit your source code to the mailing list (and put 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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