Sunday, September 13, 2009

Some ways that Perl 6 is grand, part 3 of ?

I'll be really brief this time, I promise!

Several things about Perl 6 are there to save programmer time. Some of them even will do so. ;) This week's favourite is pure laziness. Let's imagine we have one of those lists with month names in them again, and for some odd reason only want to do something to each third month.
for ^12 :by(3) {
say @months[$_];
I think that's just neat.

The caret notation is the "upto" operator, and shorthand for a range from 0 and up to its argument. So in the example above, we're asking for a range from 0 and up to 12.

The by adverbial is new in the specification. It denotes the increments for the upto operator, and allows e.g. real numbers, so that you can increment by 0.25 if it makes sense for your code to do so.

The above example then essentially iterates over 0, 3, 6, 9.

The by adverbial isn't yet implemented in Rakudo (well, duh, the spec just saw it added), where you have to settle for this for now:
for ^4 {
say @months[$_*3];
… and something different if you want to increment by 0.25. I hope you don't want to increment through the list of months by 0.25.

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