Scala, Java, Unix, MacOS tutorials (page 37)

NOTE: If you read my previous article (a Scala functional programming style To-Do List application), the new content in this article starts down at The Scala/FP Code section.

Back when I was writing Functional Programming, Simplified I started to write a little Scala/FP “To-Do List” application that you can run from the command line, based on a similar application in the Learn You A Haskell For Great Good book. For reasons I don’t remember, I decided not to include it in the book, and forgot about it until I started using GraalVM (“Graal”) recently.

I originally wrote a long introduction to this tutorial about how to work with the Scala Option/Some/None classes, but I decided to keep that introduction for a future article. For this article I’ll just say:

• idiomatic Scala code involves never using null values
• because you never use nulls, it’s important for you to become an expert at using Option, Some, and None
• initially you may want to use match expressions to handle Option values
• as you become more proficient with Scala and Options, you’ll find that match expressions tend to be verbose
• becoming proficient with higher-order functions (HOFs) like map, filter, fold, and many others are the cure for that verbosity

Given that background, the purpose of this article is to show how to use HOFs rather than match expressions when working with Option values.

Summary: This page is a printf formatting cheat sheet or reference page. I originally created this printf cheat sheet for my own programming purposes, and then thought it might be helpful to share it here.

printf: Many languages, same syntax

A great thing about the printf formatting syntax is that the format specifiers you can use are very similar — if not identical — between different languages, including C, C++, Java, Python, Perl, PHP, Ruby, Scala, Kotlin, and others. This means that your printf knowledge is reusable, which is a good thing.

I saw the following image on this Twitter page:

and immediately became curious, “How can I create something like that Ruby %Q function in Scala, but where each line becomes a string in a list, i.e., a Seq[String]?”

In my first Laminar tutorial I showed how to set up a Scala/sbt project to use Laminar to render “static” HTML code. Then in Laminar 102: A reactive “Hello, world” example, I showed how to create a small, reactive Laminar example, that sends signals from one widget to another using observables and observers.

In my experience, the next thing you’ll need to know about Laminar is routing, i.e., how to transition from one page to another in a single-page app (SPA). Therefore, in this tutorial I’ll show how to implement that for very small applications.

In my first Laminar tutorial I showed how to set up a Scala sbt project to use Laminar, and then showed a “static” example — i.e., there were no moving parts. Please see that tutorial first if you’ve never used Laminar.

BUT, because Laminar is meant for writing reactive applications with observables and observers, this tutorial begins to show its reactive concepts.

I recently started a new Scala project that uses the Scala/Scala.js Laminar library for frontend development (i.e., as a JavaScript replacement).

Laminar is a library that’s built on top of Scala.js to let you build “reactive” web applications with observables, and in this tutorial I’ll show how to create a static “Hello, world” application from scratch. Once we get past these basics, I’ll show in Part 2 of this series how to create a reactive single-page application (SPA) with Laminar.

When I first saw Scala generic type and multiple-parameter group code like this ~12 years ago, my initial thought was, “Wow, maybe I need to think about a different career”:

def race[A, B](lh: IO[A], rh: IO[B])(implicit cs: ContextShift[IO]): IO[Either[A, B]]

But in the end, as Rocky once said, it ain’t so bad. :)

For many years I struggled with how to combine two of my main interests, Zen and work. I had read that the Zen mind is the mind before thinking, so it seems like Zen and work must be totally unrelated, because you need your mind to work. And then over time I came to understand phrases like, when working, just work; in computer parlance, become single-threaded.

This article contains a collection of quotes that have been helpful to me in understanding the relationship between Zen and work. Please note that I don’t wrap each quote in double quotes, and I also try to attribute each quote to the correct author/speaker. If you’re interested in how to combine Zen and work, I hope you’ll find them helpful.

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 3.10, Using Java Collections in Scala.

Problem

You’re using Java classes in a Scala application, and those classes either return Java collections, or require Java collections in their method calls, and you need to integrate those with your use of Scala collections.

Solution

Use the extension methods of the scala.jdk.CollectionConverters object in your Scala code to make the conversions work. For example, if you have a method named getNumbers in a public Java class named JavaCollections:

I don’t watch many movies or tv shows, at least not as many as most people. The reason I don’t is because I experience lucid dreams most night that Hollywood can’t compare to. I don’t know why I have these dreams, but I have had them since I was a young child, and that’s just the way things are. This story from May 2, 2022, is just one example.

~~~

There was a bomb in the building.

Somehow I knew that.

I remember walking into a government-style building that had a parking lot directly in front of it. If you walked into the front doors, went down the hallway to the right, and then took your first left, there was a device on the floor that looked like a boxy, 1970s-style tape recorder, but it was really a bomb.

So I began working with a friend to evacuate the building. He went one way, I went the other.

As I ran around the building, Lori — my friend who died last summer — ran up to me and said in a panic, “He knows everything about you. Everything! You have to run.” I looked at her and tried to make sense of how she was here and what she was saying, but she was terrified and screamed, “RUN!” Then she ran away in the direction I had just come from.