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Operation on a Series of Integers in Perl 6

Iterating over a series of integers in a range is similar in Perl 6 to the same code in Perl 5 except of slightly different format of the foreach loop that is spelled only as for now.

• loop
• for
• foreach
• Range

my $x = 23;
my $z = 27;

for $x .. $z -> $i {
    say $i;
}

Will print the numbers 23, 24, 25, 26, 27 as expected.

C-style loop

C-style, 3-part for loops are also available in Perl 6 and they are called loop but they are not really recommended. Better to use the for loop as described above. You could say this, but it has the same issues with off-by-one errors as we have already learned to avoid in Perl 5.

my $x = 23;
my $z = 27;
loop (my $i = $x; $i <= $z; $i++) {
    say $i;
}

Series

Iterating over every 2nd number is also possible with the for loop of Perl 6 but this time, instead of 2 dots, we are using 3. Instead of a Range we are talking about a Series here.

We set the first two element of te series and the upper limit.

my $x = 23;
my $z = 27;
for $x, $x+2 ... $z  -> $i {
	say $i;
}

This will print 23, 25, 27

You could play with it more. Just one thing to remember, you have to have the upper to be exact:

for 1, 3 ... 7  -> $i {
	say $i;
}

This will work and print 1, 3, 5, 7

OTOH this

for 1, 3 ... 8  -> $i {
	say $i;
}

will freak out Rakudo which will be stuck in a loop trying to reach infinity.

And beyond.

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Written by Gabor Szabo

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Published on 2012-07-07

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