Course of Raku / Advanced / Subroutines / Nested subroutines / Exercises / Closing over the outer

Solution: Closing over the outer

Here is a possible solution to the task.

Code

sub greet($name) {
    sub message {
        "Hello, $name!";
    }

    say message;
}

greet('Anna');

🦋 You can find the source code in the file closure-over-outer.raku.

Output

Hello, Anna!

Comments

message takes no arguments, yet it can use $name. A nested subroutine closes over the lexical variables of the subroutine that contains it, so the outer $name is in scope.
When greet('Anna') runs, $name is 'Anna', so message returns Hello, Anna!. This sharing of the enclosing scope is what makes nested helpers more than just hidden functions.

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