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

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A Scala CLI 'watch' script

In the spirit of giving back whatever I can to the Scala community, here’s a very little shell script that I named scw that lets you run the scala-cli command with its --watch option:

#!/bin/sh

# NAME:    scw
# VERSION: 0.1
# PURPOSE: a script that works like a “Unix alias
#          that requires a command-line argument”.

filename=""
if [ $1 ]
then
    filename="$1"
else
    echo "PURPOSE: Run 'scala-cli <filename> --watch'"
    echo "USAGE:   scw <filename>"
    exit 1
fi

scala-cli $filename --watch

I personally used this shell script with the exercises in my Learn Scala 3 The Fast Way! book, and I’ll include it with that book’s Github repository shortly.

How to use this scala-cli shell script

I created this script because I wanted something like a Unix alias to shorten that scala-cli command. When you’re typing that command for more than 80 lessons, every character counts. :) It works like this:

$ scw Functions.sc
4
6
Watching sources, press Ctrl+C to exit.
Compiling project (Scala 3.1.1, JVM)
Compiled project (Scala 3.1.1, JVM)
4
8

Thanks to Scala CLI, that command runs my script, and when I change the script it automatically runs it again.

Scala 3: Using Term Inference with Given and Using (and extension methods)

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 23.8, Using Term Inference with Given and Using.

Scala 3 Problem

Using Scala 3, you have a value that’s passed into a series of function calls, such as using an ExecutionContext when you’re working with Scala Futures or Akka actors:

Wanting a Unix alias that takes a command-line argument (shell script, actually)

Today I wanted to create a Unix alias that took an argument (command-line argument), but from what I saw, that wasn’t going to be easy, so I created this little shell script to do what I want. It fails gracefully if you don’t supply a command-line argument, and runs the desired command if you do supply it:

#!/bin/sh

# NAME:    scw
# VERSION: 0.1
# PURPOSE: a script that works like a Unix alias
#          that requires a command-line argument

filename=""
if [ $1 ]
then
    filename="$1"
else
    echo "PURPOSE: Run 'scala-cli <filename> --watch'"
    echo "USAGE:   scw <filename>"
    exit 1
fi

scala-cli $filename --watch

I keep a bin directory in my home directory, and it’s in my PATH, so I just drop this shell script in there and then I can use it like a Unix alias.

You can also use it as an example for any similar script you want to run, i.e., a simple shell script that handles a command-line argument.

A Scala “functional programming style” To-Do List application written with Cats

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.

In functional programming, side effects are kind of a big deal

Scala: How to use higher-order functions (HOFs) with Option (instead of match expressions)

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.

Ram Dass on remembering things like Maya, Dukkha, illusion, and consciousness

Maybe because of my Back To Now app, I really like this quote about remembering from Ram Dass:

“I think that remembering is the strategy that most religions are designed to do. It’s remembering there are other planes of consciousness, it’s remembering the illusory nature. It’s remembering Maya, it’s remembering Dukkha. It’s remembering the karma, the sangha, the Buddha, it’s remembering that you’re not caught on one plane of consciousness. It’s reminding you to wake up. The device is to wake you up.”

That quote comes from this ramdass.org page.

Pink/orange Moon rising over Greater Chicagoland

I drove through Chicago recently and with my crappy old phone’s camera I got this photo of the pink and orange Moon rising over Greater Chicagoland. It was a clear night and the Moon was visible for the entire drive.

Josh McDaniels on building relationships at work

I moved to Colorado after Josh McDaniels was fired by the Broncos, and to say the least, from what I’ve heard on the local radio, he sounds like a completely different coach with the Raiders (per this SI.com article):

“One of the easy things that we’ve tried to keep in mind is we’ll get the best out of everyone here if they love coming to work every day because they love who they’re working for,” said McDaniels, sitting behind his desk. “That sounds so ridiculously simple. Seriously. But it’s the truth. If the players enjoy being coached by us the way we’re coaching them, if the coaches enjoy being treated the way they’re being treated, if the scouts and the personnel department enjoy the way that [GM] Dave [Ziegler] runs the meetings and gives everybody a voice, then when they drive in here in the morning? You should see this.”

“I’d say for me that’s from being a guidance counselor, being a teacher, those experiences,” Ziegler said. “The relationship was really what you had to solidify first to make any progress, whether you’re a classroom teacher or a guidance counselor, and you’re trying to help someone through a problem.”

“They won’t trust you if you don’t,” McDaniels said.

“As a guidance counselor, you have to create it on the front end so if there is a problem down the road, you’ve already created the relationship, so you can help someone that’s having a mental health issue, or going through something else,” Ziegler continued. “The relationship has to come first.”

A `printf` format reference page (cheat sheet) (C, Java, Scala, etc.)

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.

A Scala approach to convert a multiline string to a list (Seq[String])

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]?”

“The Man in the Arena” speech by Teddy Roosevelt

“It is not the critic who counts; not the man who points out how the strong woman stumbles, or where the doer of deeds could have done them better.”

“The credit belongs to the woman who is actually in the arena, whose face is marred by dust and sweat and blood; who strives valiantly; who errs, who comes short again and again, because there is no effort without error and shortcoming; but who does actually strive to do the deeds; who knows great enthusiasms, the great devotions; who spends herself in a worthy cause; who at the best knows in the end the triumph of high achievement, and who at the worst, if she fails, at least fails while daring greatly, so that her place shall never be with those cold and timid souls who neither know victory nor defeat.”

~ “The Man in the Arena” speech by Teddy Roosevelt, with a few minor changes, which I was reminded of by this article

Scala: A Laminar/CSS div/elements/settings example

As a brief note to self, here’s some Laminar source code that shows how to create a div in Laminar, as well as some settings/elements in that div, as well as one way to handle a reactive button click:

Laminar 103: A small reactive routing example

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.

Laminar 102: A reactive “Hello, world” example

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.

Laminar 101: A “Hello, world” example (static)

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.

How to read “difficult” Scala method type signatures

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. :)

Rocky: You ain’t so bad

Favorite quotes about work, mindfulness, and Zen

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.

MCAS/MCAD: What an activated mast cell looks like

At some point somebody was like, “Let’s get a mast cell — a type of white blood cell — from a bone marrow biopsy, magnify it 1,000 times, piss it off, and see what happens.”

The result? Ka-boom! It looks like a little firework went off when it released its histamine, tryptase, serotonin, superoxide, heparin, thromboxane, PGD2, PAF, and other granules.

That’s pretty much what it feels like, lol. I used to tell doctors that it felt like I had been drugged, and indeed, I was.

(Image from this nih.org research paper.)

MCAD: What an activated mast cell looks like

A User Story Mapping Example Using Facebook

Over on my Valley Programming website I wrote a little User Story Mapping Example Using Facebook. Whether people currently have a Facebook account or not, at one time almost everyone did, so it makes for a good example when running a story mapping workshop. See that link for more details.

Scala 3: Using Java Collections in Scala

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:

Conquer Public Speaking With the Classic Bestseller!
	How to Develop Self-Confidence and Influence People By Public Speaking