Jonathan Worthington: March 2008 Archives
Reading through the transcript of the Perl 6 call last week, I noticed that I/O was mentioned as something that Rakudo was lacking and that people were really missing. I flew to the UK on Friday, was at a wedding on the Saturday weekend and meeting up with a friend in London on the Sunday and flew back today. However, I managed to grab a few spare hours on the train on the way there, and on the Sunday evening while Normal People slept and the morning before my flight on the Monday to get some Rakudo hacking done. As a result, we now have the beginings of IO in Rakudo.
Here's a quickly hacked up random number game.
my $answer = int(rand(100)) + 1;
my $guesses = 0;
say "Guess the number (between 1 and 100)";
for =$*IN -> $guess {
$guesses++;
if $guess == $answer {
say "You got it right in $guesses guesses!";
exit
}
elsif $guess < $answer {
say "Too low";
}
else {
say "Too high";
}
}
Here's an example run of the game.
C:\Hacking\parrot\languages\perl6>..\..\parrot perl6.pbc guess.p6
Guess the number (between 1 and 100)
50
Too low
75
Too low
87
Too low
95
Too high
91
Too low
93
Too high
92
You got it right in 7 guesses!
You'll note that here I'm using $*IN. This is an instance of the IO class, so you can do:
say $*IN.WHAT;
And it will report "IO". Writing =$*IN means "get me the iterator to read from $*IN", which reads a line at a time. $*OUT and $*ERR are also available, so we can output to STDERR now by doing:
$*ERR.say("OH NOES! IT DID EXPLOSHUN!");
So we have those three file handles, but what about getting one to a file itself? That's what open is for. Here's a program that takes a file name and then prints each line in that file with the line number at the start of it.
my $fh = open(@*ARGS[0], :r); # :r = read mode
my $line = 1;
for =$fh {
say $line++ ~ " $_";
}
$fh.close();
I ran it on the readme; I'll just quote the top bit of the output.
C:\Hacking\parrot\languages\perl6>..\..\parrot perl6.pbc ln.p6 README
1 ## $Id: README 25155 2008-01-22 19:25:25Z pmichaud $
2
3 =head1 Rakudo Perl 6
4
5 This is the Perl 6 compiler for Parrot, called "Rakudo Perl 6,"
You'll notice the use of the new pair syntax for specifying the mode to open the file in, which I talked about in my last post. So already we're building stuff on top of that syntax. :-)
I'm not sure how busy the coming week will be, but I do know that next weekend and Monday are set aside for doing Perl 6 related things: I will be joining the Oslo QA Hackathon. So I look forward to seeing any of you that will be attending there, and hopefully bringing us another few steps closer to Perl 6 on Parrot.
First off, sorry it's been a while since I last posted. It's mostly been that I've just not done a lot between the Ukrainian and Dutch Perl Workshops and now, which was thanks to being busy with $REAL_LIFE and lacking either time or brain cycles for hacking Rakudo. Thankfully, I'm back into the swing of things now, and it's time to catch up on the blogging.
I'd like to give a belated thanks to everyone at the UPW and DPW for such a good time. I greatly enjoyed attending, meeting people and speaking at both workshops, and Kiev was a more beautiful city than I had imagined it being. The cathedrals and churches there are incredible - I'll surely be coming back to Ukraine to explore some more!
At UPW, some deficiencies in smart matching of arrays was discovered in Rakudo and I promised a fix. I also said I'd write a note about it here "soon", which I failed to do - sorry. I thought I had fixed array comparrison with smart match, but that appears not to be working right now. :-( Also, the Perl 5 and Perl 6 way of checking if a list contains an element are different, and the Perl 6 way was dependent on something else that wasn't implemented (though I've started work on it now, so hopefully we have that soon too). Anyway, it's on the horizon.
I'm hazy on exactly what I got done at DPW and around there, but I know I started on pairs. Thanks to some extra contributions from cognominal++, quite a lot of this is now implemented. As specifying named parameters in a sub was already done, happily it means you can now do things like:
sub sayit (:$what) { say $what; }
sayit(what => "Oo minya pivo!");
Oo minya pivo!
It also works with object instantiation too.
class Foo { has $.a }
my $x = Foo.new(a => 42); say $x.a;
42
As well as the fat arrow syntax, there's also the colon pair syntax, in various forms (we ain't got 'em all yet, but the most useful ones are there).
sayit(:what);
1
sayit(:!what);
0
sayit(:what('privyet'));
privyet
my $what = 'nyam'; sayit(:$what);
nyam
Another thing I've hacked in some basic support for is the subset keyword, which allows you to write refinement types. You can smart-match against the type name to test if the variable meets that type.
subset Guess where { $_ >= 1 && $_ <= 100 };
if 42 ~~ Guess { say "yes" } else { say "no" }
yes
if 142 ~~ Guess { say "yes" } else { say "no" }
no
if 97 ~~ Guess { say "yes" } else { say "no" }
yes
subset LowGuess of Guess where { $_ <= 50; };
if 42 ~~ LowGuess { say "yes" } else { say "no" }
yes
if 97 ~~ LowGuess { say "yes" } else { say "no" }
no
if 0 ~~ LowGuess { say "yes" } else { say "no" }
no
Hopefully more types related stuff coming soon, amongst various other things. I'll be at the Oslo QA Hackathon, and hope to get plenty of free time there, as well as generally while traveling over the coming weekends.
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