Perl 6 Deep Dive

Executing code once

In Perl 6, interestingly, it is possible to execute part of the body only once. For example, in the next loop, there should be four iterations done, but the first message will be printed only once:

for 1, 2, 3, 4 {    once {        say 'Looping from 1 to 4';    }    say "Current value is $_";}

The preceding code prints the following output:

Looping from 1 to 4Current value is 1Current value is 2Current value is 3Current value is 4

The block of code after the once keyword was executed only once.

This also works with loops of other types, for example, with the loop cycle. Considering the following code snippet:

loop (my $c = 1; $c != 5; $c++) {    once say 'Looping from 1 to 4';    say "Current value is $c";}

Notice that no curly braces are ...