These are some answers to the Week 200 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a couple of days from now (on January 22, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.

Task 1: Arithmetic Slices

You are given an array of integers.

Write a script to find out all Arithmetic Slices for the given array of integers.

An integer array is called arithmetic if it has at least 3 elements and the differences between any three consecutive elements are the same.

Example 1

Input: @array = (1,2,3,4)
Output: (1,2,3), (2,3,4), (1,2,3,4)

Example 2

Input: @array = (2)
Output: () as no slice found.

Arithmetic Slices in Raku

Seit 2011 setzt die Rother OSS GmbH mit Sitz in Süddeutschland und über das ganze Land verteiltem Team auf die Kombination aus OS-Ticketsystem und Business Services vom Experten. Konkret: Consulting, Entwicklung und Support zu den freien OTRS-Versionen.

In which we bravely overcome ambiguity, and dodge two approaches in the face of (O³).

One of the reasons I have not "moved on" from Perl to some other more "modern" language is that Perl gives me such great access to its inner workings. The Do-It-Yourself Lexical Pragmas post from a couple weeks ago is an example of this. Another example is that Perl lets you tie your own code into its warnings system.

Tying into the warnings machinery requires a module. That is, the interface assumes you are reporting problems relative to another name space that invoked your code. Your module can either add diagnostics to existing Perl warning categories or actually create new categories. In either case your diagnostics are sensitive to the enablement or disablement of the category, as well as its fatalization.

In addition to enabling or disabling warning categories, use warnings ... and no warnings ...; make some subroutines available which can be used to issue your own diagnostics. These are reported relative to the file and line that called into your module (sort of like carp()). A useful subset of the warnings:: subroutines is:

These are some answers to the Week 199 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a few days from now (on January 15, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.

Contrary to usual, I started with the Perl implementations this week (not having Raku installed on the computer where I started to work on the challenge). So I’ll present the Perl implementations first.

Task 1: Good Pairs

You are given a list of integers, @list.

Write a script to find the total count of Good Pairs.

A pair (i, j) is called good if list[i] == list[j] and i < j.

Example 1

Came across an interesting video from one of the users of Perl: Is Perl dead? @Randal L. Schwartz on Dart and Flutter @Code Maven

In which we leap tall primes in a single bound, mis-take a tree, test percussion, and find the limits of a Curious Module.

Task 1: 10001st Prime Number - One-liners (expanded) in Raku and Perl.

Task 2: Curious Fraction Tree - Solutions in Raku and Perl (with 200+ tests), and another Perl solution using a CPAN module.

Strictly speaking not news exactly, given that it dates from early 2018, but it was news to me, and since I haven’t seen it make the rounds I still find it worth disseminating. From the MySQL 8.0.11 release notes:

The utf8mb3 character set will be replaced by utf8mb4 in a future MySQL version. The utf8 character set is currently an alias for utf8mb3, but will at that point become a reference to utf8mb4. To avoid ambiguity about the meaning of utf8, consider specifying utf8mb4 explicitly for character set references instead of utf8.

This a declaration of intent rather than a change that has happened… but still. It’s been a very long September…

(To prepare for this you’ll want to note what you need to take into account regarding the way utf8mb4 and indexes interact.)

These are some answers to the Week 198 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a few of days from now (on January 8, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.

Task 1: Max Gap

You are given a list of integers, @list.

Write a script to find the total pairs in the sorted list where 2 consecutive elements has the max gap. If the list contains less than 2 elements then return 0.

Example 1

Input:  @list = (2,5,8,1)
Output: 2

Since the sorted list (1,2,5,8) has 2 such pairs (2,5) and (5,8)

Example 2

The Weekly Challenge 145

The Task 2 of the Weekly Challenge #145 asked us to build a Palindromic Tree. It also linked to a blog post explaining the "Eertree" data structure.

Maybe it was just me, but I found the blog post confusing. Fortunately, it further linked to a scientific paper that introduced the structure around 2014.

In the context of Perl, a closure is a piece of code that captures a specific instance of a lexical variable. A blog entry a month or so ago explores this in greater detail. If you review this blog entry, though, note that it does not cover lexical subroutines, which act more like anonymous subroutines even though they are named.

This blog entry, though, covers the closure warnings category.

This category has been around since warnings were introduced in Perl 5.6. I find four diagnostics in this category as of Perl 5.34.0; two related to lexical variables and two related to lexical subroutines. The "Variable" and "Subroutine" versions of these have similar causes, so I will not distinguish them in my discussion.

All of these diagnostics seem to arise from the fact that named, non-lexical subroutines are created at compile time, whereas lexical and anonymous subroutines are created at run time.

I use ot a lot when it comes to opening files. I wanted to be able to use this tool from inside vim as well. It turns out, the solution is quite simple.

Full post: https://www.olafalders.com/2022/01/05/open-this-file-from-inside-vim/

These are some answers to the Week 197 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a couple of days from now (on January 1, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.

Task 1: Move Zero

You are given a list of integers, @list.

Write a script to move all zero, if exists, to the end while maintaining the relative order of non-zero elements.

Example 1

Input:  @list = (1, 0, 3, 0, 0, 5)
Output: (1, 3, 5, 0, 0, 0)

Example 2

Input: @list = (1, 6, 4)
Output: (1, 6, 4)

Example 3

Input: @list = (0, 1, 0, 2, 0
Output: (1, 2, 0, 0, 0)

Testing

It's time to test what we have written so far. If you look at the asar project, there are already some test files and they come with their own test syntax. It's actually pretty neat since it's embedded in the ASM files comments, so you don't need to write specific tests files.

The format is documented here https://github.com/RPGHacker/asar#test-format but for now, we will just keep the offset and byte value part.

Testing grammar

We could write a loop with like files.IO.slurp.lines and be done to handle this. But let use again a grammar. No action associated with it since it's very basic.

The phrase "Lexical Pragmas" is probably both redundant and ungrammatical (the correct plural of "pragma" being "pragmata", I believe). But the use of "pragma" to mean "Perl module with an all-lower-case name" is fairly common, and I wanted to make clear that this was not what I was talking about. This blog entry is about writing Perl code whose configuration changes are limited to a lexical scope, just like built-in pragmata such as strict or warnings.

There are two pieces to the puzzle: storing the configuration (at compile time) and reading the configuration.

Perl

I had a reasonably productive year, releasing several modules that I think/hope are useful for the wider ecosystem.

Crypt::Passphrase

This module manages the passwords in a cryptographically agile manner. That means that it can not only verify passwords using different ciphers, but it also aids in gradually upgrading passwords hashed with an outdated cipher (or outdated settings) to the current one; for example when you want to upgrade from bcrypt to argon2. Password hashing is both a rather common form of cryptography, and one that is more subject to change than others; you should probably reevaluate your password handling every couple of years. With this module, you can initiate such a transition with a simple configuration change.

This also includes a number of extension distributions (e.g. Crypt::Passphrase::Argon2, Crypt::Passphrase::Bcrypt, etc…), and one new backend module (Crypt::Bcrypt)

Thread::Csp

These are some answers to the Week 196 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a few days from now (on December 25, 2022 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.

Task 1: Pattern 132

You are given a list of integers, @list.

Write a script to find out subsequence that respect Pattern 132. Return empty array if none found.

Pattern 132 in a sequence (a[i], a[j], a[k]) such that i < j < k and a[i] < a[k] < a[j].

Example 1

Input:  @list = (3, 1, 4, 2)
Output: (1, 4, 2) respect the Pattern 132.

Example 2

Input: @list = (1, 2, 3, 4)
Output: () since no susbsequence can be found.

Example 3

Please go here instead.

Hello fellow Dancers!

I have posted a draft deprecation policy for the Dancer2 code base for public review.

The Dancer Core Team has done our best to look at this every which way and cover all potential issues and use cases, but we're sure to have missed something here or there. So take a look and let us know. Your feedback is welcome - please add comments, feedback, and suggestions on the issue.

Thanks in advance! :-)

Time to relax before ...

What a shame, I delayed the Monthy Report once again. Although I did manage to publish last month on time i.e. 4th Nov.

Do I have reason to justify the delay?

Well, December, is always the busiest month. It is the month when I spend more time with family than ususal. Also I was busy with the Advent Calendar 2021.

As you must have guessed, today I am done with the final gift. Hence, the monthly report is getting time. There was another reason for the delay as I started Live Coding again. I have done few, which I will talk about in the end of year report in a week time, insha-ALLAH.

So, what was the highlight of last month?