This is my second blog for The Weekly Challenge. I am only able to participate, thanks to Ryan Thompson for helping me with the Perl and Raku reviews. I am going for Perl solutions first then will try to translate it into Raku next. I believe in coding to learn the language. With so many Raku experts around, I am not shy throwing questions up. I am now going to share my experience doing “The Weekly Challenge - 049”.

Challenge #049 (Task #1)

#!/usr/bin/perl

use strict;
use warnings;

my $num = $ARGV[0];
die "Missing number.\n" unless defined $num;

my ($res, $i);
do { $res = $num * ++$i; } until ($res =~ /^[01]+$/);
print "$num => $res\n";

Challenge #049 (Task #2)

Technically I cheated and took the help of CPAN module Cache::LRU. However it makes the end result so clean and tidy. It just worked out of the box. I just had to hack to handle the missing key return value. By design Cache::LRU returns undef, if it can’t find the key. As per the task, I had to print -1 instead, hence the hack came in action. Otherwise it is self explanatory.

#!/usr/bin/perl

use strict;
use warnings;

use Cache::LRU;

my $cache = Cache::LRU->new(size => 3);

$cache->set(1 => 3);
$cache->set(2 => 5);
$cache->set(3 => 7);

print "get(2) => ", $cache->get(2), "\n";
print "get(1) => ", $cache->get(1), "\n";

print "get(4) => ", $cache->get(4)||-1, "\n";

$cache->set(4 => 9);

print "get(3) => ", $cache->get(3)||-1, "\n";

Now the fun part to translate the Perl solution to Task #1.

Here is my first draft in Raku

#!/usr/bin/env perl6

use v6;

sub MAIN($num) {
    my (Int $res, Int $i);
    repeat { $res = $num * ++$i } until $res ~~ /^[01]+$/;
    $res.say;
}

Now running the script gets the following response:

$ perl6 ch-1.p6
Usage:
  ch-1.p6 <num>
$

What if we pass non-integer command line parameter:

$ perl6 ch-1.p6 dummy
Cannot convert string to number: base-10 number must begin with valid digits or '.' in '⏏a' (indicated by ⏏)
  in sub MAIN at ch-1.p6 line 7
  in block <unit> at ch-1.p6 line 5

Lets force the data type of command line parameter:

#!/usr/bin/env perl6

use v6;

sub MAIN(Int $num) {
    my (Int $res, Int $i);
    repeat { $res = $num * ++$i } until $res ~~ /^[01]+$/;
    $res.say;
}

Now lets check what difference it made:

$ perl6 ch-1.p6 dummy
Usage:
  ch-1.p6 <num>

I am now happy with the response. I am now ready for real test.

$ perl6 ch-1.p6 5

It just goes into the wild without giving any result. I am confused what’s goind on here. I started looking for reason and found out that my regex is causing this behaviour. So I modified it like below.

#!/usr/bin/env perl6

use v6;

sub MAIN(Int $num) {
    my (Int $res, Int $i);
    repeat { $res = $num * ++$i } until $res ~~ /^<[01]>+$/;
    $res.say;
}

Now running the script again:

$ perl6 ch-1.p6 5
10
$

What did I learn today?

a) Command line parameter data type handling.

b) The loop construct repeat { } until as per the documentation.

c) Regex using with < and >.

I don’t think I can do the Task #2 in Raku yet. May be next time.