Once a Week a happy zef

Since zef installs modules to a temporary directory and may or may not set the $*CWD to what we would like, we need to open files in tests carefully. Given that files of interest to a test file are in the same or a child directory of the test, we can operate relative to $*PROGRAM.

my $gitconfig-path = $*PROGRAM.parent.child('data').child('gitconfig');

That would translate to t/data/gitconfig seen from the modules base directory.

Once a Week

Rakudo is still changing quickly for the betterment of mankind (I’m quite sure of that). Once in a while commits will break code that is or was working. Checking for regressions is boring because most of the time it wont happen. As the army of bots that populate #perl6 shows, we like to offload the housekeeping to software and for testing we use travis.

Since a while travis provides build in cronjobs for rebuilding repos automatically. It’s a little hidden.

I missed the cron settings at first because one needs to run a build before it even shows up in the settings tab.

With cron jobs setup to test my modules once a week I will get some angry e-mails every time Rakudo breaks my code.

After clicking the same buttons over and over again I got bored and found the need to automate that step away as well. A meta module that doesn’t do anything but having dependencies to my real modules would save me the clicking and would produce exactly one angry e-mail, what will become more important as the Perl 6 years pass by. The .travis.yml looks like this:

language: perl6
sudo: false
perl6:
- latest
install:
- rakudobrew build-zef
- zef --debug install .

And the META6.json is:

{
"name" : "gfldex-meta-zef-test",
"source-url" : "git://github.com/gfldex/gfldex-meta-zef-test",
"perl" : "6.c",
"build-depends" : [ ],
"provides" : {
},
"depends" : [ "Typesafe::XHTML::Writer", "Rakudo::Slippy::Semilist", "Operator::defined-alternation", "Concurrent::Channelify", "Concurrent::File::Find", "XHTML::Writer", "Typesafe::HTML" ],
"description" : "Meta package to test installation with zef",
"test-depends" : [ ],
"version" : "0.0.1",
"authors" : [
"Wenzel P. P. Peppmeyer"
]
}

And lo and behold I found a bug. Installing XHTML::Writer on a clean system didn’t work because zef uses Build.pm differently then panda. I had to change the way Rakudos lib path is set because zef keeps dependency modules in temporary directories until the last test passed.

my @include = flat "$where/lib/Typesafe", $*REPO.repo-chain.map(*.path-spec);
my $proc = run 'perl6', '-I' «~« @include, "$where/bin/generate-function-definition.p6", "$where/3rd-party/xhtml1-strict.xsd", out => $out-file, :bin;

Please note that Build.pm will be replaced with something reasonable as soon as we figured out what reasonable means for portable module building.

There is a little bug in zef that makes the meta module fail to test. Said bug is being hunted right now.

All I need to do to get a new module tested weekly by travis is to add it to the meta module and push the commit. Laziness is a programmers virtue indeed.

Leaving out considered dangerous

A knowledge seeker asked us why a loop spec allows $i>10 but not $i<10. The reason is that the postcircumfix:«< >» changes the grammar in such a way that it expects a list quote after the $i. As a result you get the following.

loop (my $i=0;$i<10;$i++) {};
# OUTPUT«===SORRY!=== Error while compiling ␤Whitespace required before < operator␤at :1␤------> loop (my $i=0;$i<10;$i++) {};⏏␤    expecting any of:␤        postfix␤»

I tried to illustrate the problem by making the $i>10 case fail as well by defining a new operator.

sub postcircumfix:«> <»($a){}; loop (my $i=0;$i>10;$i++) {};
# OUTPUT«===SORRY!=== Error while compiling ␤Unable to parse expression in postcircumfix:sym«> <»; couldn't find final $stopper ␤at :1␤------> rcumfix:«> <»($a){}; loop (my $i=0;$i>10⏏;$i++) {};␤    expecting any of:␤        s…»

I concluded with the wisdom that that Perl 6 is a dynamic dynamic language. While filing a related bug report I made the new years resolution to put a white space around each and every operator. You may want to do the same.

Perl 6 is Smalltalk

Masak kindly pointed the general public to a blog post that talks about how awesome Smalltalk is.
The example presented there reads:

a < b
  ifTrue: [^'a is less than b']
  ifFalse: [^'a is greater than or equal to b']

The basic idea is that ifTrue and ifFalse are methods on the class Bool. Perl 6 don’t got that and I thought it would be tricky to add because augment enum doesn’t work. After some tinkering I found that augment doesn’t really care what you hand it as long as it is a class. As it happens Rakudo doesn’t check if the class is really a class, it simply looks for a type object with the provided name. The following just works.

use MONKEY-TYPING;
augment class Bool {
    method ifTrue(&c){ self ?? c(self) !! Nil; self }
    method ifFalse(&c){ self ?? Nil !! c(self); self }
}

(1 < 2)
    .ifTrue({say ‚It's True!‘})
    .ifFalse({ say ‚It's False!‘});

If we call only one of the new methods on Bool, we could even use the colon form.

(True)
    .ifTrue: { say "It's $^a!" };

As you likely spotted I went a little further as Smalltalk by having the added methods call the blocks with the Bool in question. Since Block got a single optional positional parameter the compiler wont complain if we just hand over a block. If a pointy block or a Routine is provided it would need a Signature with a single positional or a slurpy.

Please note that augment on an enum that we call a class is not in the spec yet. A bug report was filed and judgement is pending. If that fails there is always the option to sneak the methods into the type object behind Bool at runtime via the MOP.

And so I found that Perl 6 is quite big but still nice to talk about.

UPDATE: There where complains that IfTrue contained an if statement. That’s was silly and fixed.