Course of Raku / Essentials / Loops

Using until

The until construct is opposite to while. It executes the block of code until the condition becomes True (or, in other words, while it is False).

Here is a modified program from the previous page that uses until and a new condition:

my $x = 0;
until $x > 10 {
    $x = prompt 'Enter a number, which is not bigger than 10: ';
    say "You entered $x.";
}
say "$x is bigger than 10.";

Run the program and check the output:

$ raku t.raku 
Enter a number, which is not bigger than 10: 10
You entered 10.
Enter a number, which is not bigger than 10: 4
You entered 4.
Enter a number, which is not bigger than 10: 1
You entered 1.
Enter a number, which is not bigger than 10: 20
You entered 20.
20 is bigger than 10.

until vs. while

Compare the equivalent programs with while and until:

while $x <= 10 { . . . }

until $x > 10 { . . . }

As you see, the conditions are negated versions of each other. In this sense, while and until are in the same relations as if and unless.

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