Course of Raku / Functional, concurrent, reactive, and web programming / Functional programming / Lambdas and closures / Exercises / A counter

Solution: A counter

Here is a possible solution to the task.

Code

sub make-counter($step) {
    my $n = 0;
    return sub { $n += $step };
}

my &count = make-counter(10);
say count();
say count();
say count();

🦋 You can find the source code in the file counter.raku.

Output

10
20
30

Comments

The closure captures two things from make-counter: the parameter $step and the private variable $n. Both stay alive after make-counter returns.
Each call adds $step to $n and returns the new total. A counter built with a different step would advance by that amount instead.

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