blogs.perl.org

In this post I'll talk about what I hacked on the second day of the SUSE hackweek. If you missed my other posts:

• Day 1 - Perl ♥ Bash
• Day 3 - (Not) Loading Objects in YAML::PP
• Day 4 - Fighting with XS and C

This week, there was more work to be done for some of us: in addition to the standard three challenges, there was one more from Neil Bowers. His suggestion for a challenge had been simplified, so he published the original specification.

Van Eck’s Sequence

Let a₀ = 0. Then, for n ≥ 0, if there exists an m < n such that a_m = a_n, take the largest such m and set a_n+1 = n − m; otherwise a_n+1 = 0.

I didn’t find a non-recursive formula for the sequence. I implemented a solution using an iterator: a subroutine that returns the next element of the sequence on each call.

Let’s start with a test.

Why Perl 5 benefits is never talked in Perl Weekly Challenge?

The second task of last week's Weekly Challenge
was to list the dates of the last Friday in every month of a given year.

Many of the participants went to great lengths to create efficient and accurate solutions:
tracking the last day of each month, detecting leap years correctly,
working out formulas for the day of the month for a particular date,
managing the complex date arithmetic required.

But, given the powerful Date class built into Raku, most of those
admirable exertions were not actually necessary.

The entire task could be accomplished simply by walking through
from 1 January to 31 December of the given year, first checking
if each date is a Friday (i.e. the "day of the week" value is 5), and then
checking if the following Friday (i.e. the date exactly one week later)
happens to fall in a different month.

If both of those criteria are true, then we have a "last Friday of the month",
so we simply print it.

In other words:

This week we had the SUSE Hackweek 18. It was my first Hackweek since I started working for SUSE. It happens about once or twice a year. People can contribute to any open source project they want to in that week.

So, thanks to SUSE for making this happen!

This blog post is about what I hacked on Tuesday, when Hackweek started for me. Expect more posts for the other days ;-)

• Day 2 - YAML::PP !include
• Day 3 - (Not) Loading Objects in YAML::PP
• Day 4 - Fighting with XS and C

Originally posted on officially website, here I share the journey so far.

Challenge 1: Write a script to print the date of the last Friday of every month in a given year

First thought was to use a module to look up the day of the week for the last day of each month in the given year, then work backwards (in each month) to get the last Friday. But — well, once the weekday of any day in the year is known, the rest can be calculated directly without a further module look-up.

Actually, no module look-up is really needed at all once the day-of-the-week of any day in any year is known. And since I know that 17^th June, 2019, is a Monday, I should be able to derive the solution from first principles, as it were, by counting backwards or forwards as needed. But working out leap years is tricky! So I compromised: one look-up for each given input year.

Perl 5 solution

Search is a hard problem. It is the task of getting users to what they want to find, even if they don't know exactly what that is. Its requirements vary widely based on the kinds of things people will want to find and the kinds of people that want to find them. It's also an expected feature of almost anywhere on the web that is more complex than a single page. So shortly after putting together a demo for Perldoc Browser which would become the backend for perldoc.pl, I needed to make it searchable.

Last Fridays

Write a script to print the date of last Friday of every month of a given year.

To handle dates, I used Time::Piece, a core module since 5.10. It has no method to get the last Friday of a month directly, so I tried a simple trick: get the first day of the next month, subtract one day, and continue to subtract days until we get a Friday.

Time::Piece does all the date maths in seconds. I also used Time::Seconds to get the constant ONE_DAY so I didn’t have to count it myself (60 * 60 * 24, right?)

On behalf of the Dancer Core Team, I would like to announce the release of Dancer2 0.20800 (the TPCiP release). This version introduces a new keyword, prepare_app, and features a small handful of bug and documentation fixes.

We have found a growing number of instances where not having the ability to execute code on application load is a real annoyance. The prepare_app keyword will allow you to run a block of code when your app is loaded, and is inspired from Plack's prepare_app method. Thanks, Sawyer, for making this happen.

The full changelog is as follows:

These are some answers to the Week 13 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in several days from now (June 23, 2019). This blog post offers some solutions to this challenge, please don't read on if you intend to complete the challenge on your own.

Challenge # 1: Thank God, It's Friday

Write a script to print the date of last Friday of every month of a given year. For example, if the given year is 2019 then it should print the following:

Sigh. It's always the way, isn't it?

You no sooner get done writing about how having the right tools can make a particular coding task trivially easy...when you realize that, right next door, there was a much better example you could have used to make exactly the same point.

The "longest initial subpath" example I talked about in my previous post was challenge #2 of last week's Weekly Challenge. But challenge #1 that week makes it even clearer how much the right tool can simplify a task.

Challenge #1 was to find the smallest Euclid number that isn't a prime. The Nth Euclid number is given by the product of the first N primes, plus one. So the sequence of Euclid numbers is:

(2)+1, (2*3)+1, (2*3*5)+1, (2*3*5*7)+1, (2*3*5*7*11)+1, ...

In November 2015 I started my App::Spec commandline framework and wrote this blogpost.

It's not only a framework for perl. It can also generate shell tab completion for other tools.

Since then I have been busy with other things, but recently continued working on it for several reasons, and fixed several bugs, mostly for bash.

Last year I started a collection of generated completion scripts for bash and zsh:

https://github.com/perlpunk/shell-completions

Today it contains completions for 20 tools, mostly for perl commands. If you miss a tool there, let me know, or try to write your own YAML specification and generate the completion.

Below you will see some examples.

How to display NA in CPAN Testers?

I asked qustion "I want to display NA instead of UNKKONW in CPAN Testers"

I get some answers.

Thank you for everone!

I write a example to to display NA in CPAN Testers.

The Smallest Non-Prime Euclid Number

An Euclid number is a number that equals 1 + product of a sequence of primes.

To speed things up, I used an object that caches the sequence of primes discovered so far. The method size returns the length of the sequence of primes; extend_to extends the sequence up to the specified number.

A few years ago, I created a talk (and later an entire class) about "transparadigm programming" in Raku.

The basic premise was that while some languages restrict you to only a single hammer (or worse: a box full of hammers), Raku was designed to be a complete toolkit: integrating OO, functional, concurrent, declarative, and procedural tools to allow you to choose exactly the right combination for each job.

That idea came back to me in full force recently. In last week's Weekly Challenge, the second task was to take a list of file paths and find the longest common initial subpath (i.e. the deepest directory they all share).

The solutions offered by the various registered participants were all very clean, and often both efficient and elegant. Yet most of them were variations on the same procedural solution: Split each path on the directory separator, then for 1-to-N: compare all the Nth components and quit if they're not identical. Something like:

These are some answers to the Week 12 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in several days from now (June 16, 2019). This blog post offers some solutions to this challenge, please don't read on if you intend to complete the challenge on your own.

Challenge # 1: Euclid's Numbers

The numbers formed by adding one to the products of the smallest primes are called the Euclid Numbers (see wiki). Write a script that finds the smallest Euclid Number that is not prime. This challenge was proposed by Laurent Rosenfeld.

I did not even remember I proposed this challenge to my friend Mohammad Anwar.

Can meta cpan display html table.

metaCPAN support img tag.

https://metacpan.org/pod/Chart::Clicker

If I use HTML table in pod,

<table>
  <tr>
    <th>title1</th>
    <th>title2</th>
   </tr>
  <tr>
    <td>foo</td>
    <td>bar</td>
  </tr>
</table>

If you know, tell me the answer.

From the website's blurb:

You might find my Roles and Responsibilities in Scrum of interest (Scrum is not Waterfall).