Learning Perl 6 by playing silly games

Posted on 07 September 2010

So I decided to take the plunge and see what Rakudo* has to offer and what Perl 6 is like as a language. I’ve always found the best way to learn programming is through examples and by doing tasks, so when I found the perl6-examples collection, I started to go through the 99-problems one by one.

Although I started out writing “baby” perl 6, I quickly found that other people’s solutions to the problems were shorter – and clearer – than my own. It’s quickly become clear that the menagerie of perl 6 operators is more expressive than I ever imagined possible. I’ve never complained that a language lacked a particular operator, or that a language should be extended by adding more operators. Perl 6 may be changing my mind.

Today all this was made clear by a silly example in #perl6: noughts and crosses! (or tic-tac-toe, if you prefer.) The problem: given a noughts-and-crosses grid, where the players are 1,-1 and the empty squares 0, determine who, if anyone, has won. Here’s the first example that masak made:

He uses a slicel function to create cross-cutting slices of multidimensional arrays, and uses his list of lines to go through all possibilities, finding a winner. He also takes advantage of the [==] reduction metaoperator: [==] results in a == b && b == c. The reduction metaoperator can also create such useful functions as [+] sum and [*] product, which in other languages would require a separate function call. In Perl 5, for example, product is reduce { $a * $b } using reduce from List::Util.

Here’s my improvement:

By flattening the board array, I avoided the need for a slicel function; I also used the X+ cross metaoperator to shorten creating the lines. Xop <1 2 3> gives a op 1, a op 2, a op 3, b op 1, b op 2, b op 3, c op 1, c op 2, c op 3. Then moritz_ pointed out that 0,1,2 can be written using the upto operator: ^3:

Further refinements are possible: 0,3,6 is ^3 »*» 3, using the hyper operator to multiply each of 0,1,2 by 3. But by this point, we’re just using different Perl 6 operators for the sake of it, not because it makes the code clearer. Like code golf, this is hackers at play; and while the product is not something necessarily useful, the learning I’ve gained from it is invaluable.