27. Prime numbers

Decide if the given number is a prime number.

Prime numbers are those that can be divided only by 1, and by themselves.

The language provides us with a built-in support, the is-prime routine, for checking if the number is prime. There are two ways of using it.

First, as a built-in function:

say 'Prime' if is-prime(17);

Second, as a method on an object of the Int type:

my $n = 15;
say $n.is-prime
    ?? "$n is prime"
    !! "$n is not prime"
    ;

Here, the ternary operator ?? … !! is used. This code prints either of the strings, depending on the result of calling $n.is-prime:

17 is prime

15 is not prime

Notice that the is-prime routine contains a hyphen in its name, which is a valid character for identifier names in Raku.

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