Comments on: Day 9: Having beautiful arguments (and parameters)

By: carl

carl — Tue, 14 Dec 2010 15:21:49 +0000

Oops, that was a thinko on my part — the &action does need to be specified. Now corrected in the post. Thanks.

A few random comments: a Perl 6 compiler with the appropriate presence of mind would flag such an omission at compile time. (There’s no such compiler yet, but it’s definitely possible.) Regardless, the code wouldn’t make it through runtime since the signature binding would fail.

I was once sitting at a dinner table opposite Damian Conway and Larry Wall. Larry was pondering adding a special code-parameter, as in Ruby, with a special syntactic exception so that omission of a comma for a block specified inline would not be an error, as it is now in Perl 6. That idea was just idle speculation, though, and hasn’t made it into spec.

By: szeryf

szeryf — Tue, 14 Dec 2010 15:13:41 +0000

Why isn’t the action parameter used in recursive calls to traverse_inorder? Is the code-parameter special (as in Ruby)? Or (if it’s normal) can we use more than one code-parameter (unlike in Ruby)?

By: carl

carl — Thu, 24 Dec 2009 09:30:58 +0000

I think the point where I really fell in love with the short form of named parameters was when I realized that they can be used even with variables that have a twigil (secondary sigil) -- for the purposes of the parameter naming, it's simply ignored. So these examples all work: sub outer { inner(:$^some-arg); } # :some-arg($^some-arg) configure-io(:$*IN); # :IN($*IN) method build() { precompute-stuff(:$!a, :$!b, :$!c); } # :a($!a) etc.

By: Daniel Brockman

Daniel Brockman — Thu, 24 Dec 2009 02:01:01 +0000

A similar short form for named parameters exists in O’Caml:

To pass 123 as the value of the named parameter “foo”, you use this syntax:

~foo: 123

But if you have 123 stored in a variable called “foo”, you can simply do this:

~foo

It’s very, very convenient, and it also all but forces you to name your variables and parameters thoughtfully and consistently. Good move to include this feature in Perl 6.

By: ?

Wed, 09 Dec 2009 20:43:42 +0000

This is probably much better:

$_ = sprintf(“%b”, $_) and tr/01/ #/ and print $_, “\n” for “734044754508967647390469414544647854399310″ =~ /(.{7})/g;

I’m looking forward to having chained operations so much nicer in Perl 6.

By: carl

carl — Wed, 09 Dec 2009 14:40:16 +0000

The short form of named arguments is really, really nice. Not least because it interacts seamlessly with twigils (by ignoring them) — something that only becomes a desired feature after a while, when you suddnely think “hm, will it work if I do this? It cannot possibly work if I do this…” …and it does!

foo(:$*global, :$^placeholder, :$!attr, :$.accessor);

By: bened

bened — Wed, 09 Dec 2009 14:09:30 +0000

$middle .= substr(0, 1);
-> Started reading this like Perl 5 before I realized the new meaning. : )

I’m really impressed with the short form of named parameters. I think no other language could possibly do this right now. (Well, maybe you could do it in Common Lisp with macros.)

By: Moritz

Moritz — Wed, 09 Dec 2009 09:25:11 +0000

There’s a branch in Rakudo where lots of things are reworked (the ‘ng’ branch, if anybody is curious). On that this piece of code faithfully reports Cannot assign to readonly value.

We expect that branch to land some time this month, or at the very latest due to the release in January.

By: Moritz

Moritz — Wed, 09 Dec 2009 09:22:05 +0000

Instead of split and grep you can also use "73..." =~ /(.{7})/g, to stay closer to the Perl 6 version :-)

By: ?

Wed, 09 Dec 2009 08:44:27 +0000

If you’re a Perl 5 user, and feel left out looking at the last one-liner, here’s something roughly equivalent:

print(($_ = (sprintf(“%b”, $_))) =~ tr/01/ #/ && $_, “\n”) for grep { $_ ne “” } split /(\d{7})/, “734044754508967647390469414544647854399310″;

I won’t admit it’s the best way to get it in Perl 5 as a one-liner…