Day 21: Raku and I: Journey begin …

It has been ages since I last blogged about Raku. The only time, I have blogged about when I took part in The Weekly Challenge. But then this also changed recently as I finally found time to contribute to the weekly fun challenges but no blogging still.

I would say it is all about my mental state, since I have so much to talk about. Recently I was approached by a very dear friend and senior member of Raku Community if I am interested in contributing to the Raku Advent Calendar 2022. So as you guessed it rightly so, I have a compelling reason to get back to blogging.

But then you know ….

I always have too many things on my plate, so getting done something new is always tricky. However I had made up my mind, no matter what I would give it my best shot.

Here I am …

So what am I going to talk about then?

Those who know me personally, are aware that I am a Perl guy by nature. Having said, I started playing with other languages recently thanks to the vibrant group of Team PWC. In this blog post, I would like to talk about some of my contributions to the weekly challenge in the new found love Raku language.

1: Prime Sum

You are given a number $N. Write a script to find the minimum number of prime numbers required, whose summation gives you $N.

With the power of Raku built-in features, it is a piece of cake, if you know what you are doing. For me, the official Raku Documentation is the answer to all my questions. And if I can’t find what I am looking for then I ask my friends on various social platform. 9 out of 10 times, I get the answer instantly.

So in this case, all the hard work is done by is-prime. I am a big fan of method chaining as you can see below. Just for the sake of the reader, I go through the list 2..$sum and grep everything that is-prime.

Isn’t beautiful? For me, it is.

sub find-prime-upto(Int $sum) {
    return (2..$sum).grep: { .is-prime };

Now with the handy subroutine ready, we are read to solve the task as below:

For my Perl friends new to Raku, the only thing might trouble you is the use of [+], right?

It is the Reduction Operator [] that works on lists of values.

sub prime-sum(Int $sum) {

    my @prime = find-prime-upto($sum);
    my @prime-sum = Empty;
    for 1..$sum -> $i {
        for @prime.combinations: $i -> $j {
            my $_sum = [+] $j;
            @prime-sum.push: $j if $_sum == $sum;

    return @prime-sum;

Now glue together everything as below:

use v6.d;

sub MAIN(Int $SUM where $SUM > 0) {

Still not done yet as unit test is nice to have.

use Test;

is-deeply prime-sum(6).<>,  [],                  "prime sum = 6";
is-deeply prime-sum(9).<>,  [(2, 7),],           "prime sum = 9";
is-deeply prime-sum(12).<>, [(5, 7), (2, 3, 7)], "prime sum = 12";


2: Fibonacci Sum

Write a script to find out all possible combination of Fibonacci Numbers required to get $N on addition.

You are NOT allowed to repeat a number. Print 0 if none found.

You may find the solution below somewhat similar to the above work but there is something new for Perl fans. In Perl we can get the last element of a list $list[-1] but in Raku it is slightly different as you see below.

One more thing, if you look at closely the parameter checks done in the signature itself which we don’t have in Perl.

Raku rocks !!!

sub fibonacci-series-upto(Int $num where $num > 0) {
    my @fibonacci = (1, 2);
    while @fibonacci.[*-1] + @fibonacci.[*-2] <= $num {
        @fibonacci.push: @fibonacci.[*-1] + @fibonacci.[*-2];

    return @fibonacci;

Now we are ready to solve the task as below:

Did you notice something special here?

Yes, .combinations. Again all built-in, no need to import any library. It generates all possible combinations of given size.

sub fibonacci-sum(Int $sum where $sum > 0) {

    my @fibonacci     = fibonacci-series-upto($sum);
    my @fibonacci_sum = Empty;
    for 1 .. $sum -> $i {
        last if $i > @fibonacci.elems;
        for @fibonacci.combinations: $i -> $comb {
            my $_sum = [+] $comb;
            @fibonacci_sum.push: $comb if $_sum == $sum;

    return |@fibonacci_sum;

Final application.

use v6.d;

sub MAIN(Int :$N where $N > 0) {

Time for some unit test too.

use Test;

is-deeply fibonacci-sum(6), ((1,5), (1,2,3)), "fibonacci sum = 6";
is-deeply fibonacci-sum(9), ((1,8), (1,3,5)), "fibonacci sum = 9";


3: Count Set Bits

You are given a positive number $N.

Write a script to count the total numbrer of set bits of the binary representations of all numbers from 1 to $N and return $total_count_set_bit % 1000000007.

For this task, Raku has most of the funtions built-in, so nothing to be invented.

As you see, it is one-liner, (1..$n).map( -> $i { $c += [+] $i.base(2).comb; }); where all the work is done.

.map() works same as in Perl. In this case each element gets assigned to $i. Further on $i gets converted to base 2 i.e. binary form then finally split into individual digits using .comb.

How can you not fall in love with Raku?

sub count-set-bits(Int $n) {
    my $c = 0;
    (1..$n).map( -> $i { $c += [+] $i.base(2).comb; });
    return $c % 1000000007;

Unit test to go with it.

use Test;

is count-set-bits(4), 5, "testing example 1";
is count-set-bits(3), 4, "testing example 2";


4: Smallest Positive Number

You are given unsorted list of integers @N.

Write a script to find out the smallest positive number missing.

This task introduced me something new that I wasn’t aware of earlier.

I always wanted to put check on the elements of input list. In this task, I am checking every elements in the given input list is integer. Also the return value is of type integer too. All these done with one line @n where .all ~~ Int --> Int. This is the power of Raku we can have the power in our script.

Also to sort a list, just use .sort together with .grep makes it very powerful.

The .elems gives me the total number of elements in the list.

sub smallest-positive-number(@n where .all ~~ Int --> Int) {

    my @positive-numbers = @n.sort.grep: { $_ > 0 };
    return 1 unless @positive-numbers.elems;

    my Int $i = 0;
    (1 .. @positive-numbers.tail).map: -> $n {
        return $n if $n < @positive-numbers[$i++]

    return ++@positive-numbers.tail;

Final application looks like below.

Did you see something new?

Well, it shows how to set the default parameter values.

use v6.d;

sub MAIN(:@N where .all ~~ Int = (2, 3, 7, 6, 8, -1, -10, 15)) {
    say smallest-positive-number(@N);

Time for unit test again.

use Test;

is smallest-positive-number((5, 2, -2, 0)),  
   1, "testing (5, 2, -2, 0)";
is smallest-positive-number((1, 8, -1)),     
   2, "testing (1, 8, -1)";
is smallest-positive-number((2, 0, -1)),     
   1, "testing (2, 0, -1)";



Learning Raku is an ongoing journey and I am loving it. I haven’t shared everything to be honest. If you are interested then you can checkout the rest in my collections.

Enjoy the break and stay safe.

2 thoughts on “Day 21: Raku and I: Journey begin …

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