Posts in the “scala” category

A Scala shell script example (and discussion)

Scala shell script FAQ: How do I create a Unix/Linux shell script to run a small Scala script?

If you want to run a Scala script as a Unix or Linux shell script -- such as -- write your script like this:

Getting a random element from a list of elements in Scala

In working on projects like SARAH and other apps where I try to make a computer seem more “human,” I’ve been making my software reply to me in random ways. What I’ve found is that this ends up being an easily repeatable pattern, where you have a list of possible replies, and then you randomly return one of those replies.

Scala/Java/Kotlin dates FAQ: How do I calculate the difference between two dates (LocalDate, ChronoUnit)

Scala dates FAQ: How do I calculate the difference between two dates? That is, while using Scala 2 or Scala 3, you need to determine the difference between two dates. Also, you want to use the newest Java date/time API for this work, such as the date/time API in Java 8, 11, 14, 17, etc.

Solution: Calculating the difference between two dates (in Scala and Java)

If you need to determine the number of days between two dates in Scala — or Java or Kotlin — the DAYS enum constant of the java.time.temporal.ChronoUnit class provides the easiest solution:

The ZIO 2 “mental model”

As I work more with ZIO 2, I also find myself thinking a lot about the ZIO 2 mental model, by which I partially mean “a way of thinking about your code” and also “ZIO 2 best practices.”

Here are my initial notes. Also, I hope that most of this code is mine, but several snippets are from other sources that I don’t remember, including the official ZIO 2 docs.

A ZIO 2 cheatsheet

April, 2024 Update: This ZIO cheatsheet is currently being updated to ZIO 2.x, but it still needs a lot of work.

If you want a good cheat sheet right now, see this one on github. I’m creating my own as I learn ZIO and read the ZIOnomicon book. During the learning process I find that it’s much better to create your own by hand, that way you get something that’s meaningful to you.

Note that almost all of these initial examples come from the ZIOnomicon book and the video that I link to later.

The ZIO Scaladoc

Here’s a link to the ZIO Scaladoc. That’s for the companion object, and this link is for the companion trait.

Scala Either type: How to get the value out of an Either

Scala Either FAQ: How do I get the value out of a Scala Either?


In this recipe I show many different ways to get the value out of a Scala Either, while accounting for the fact that an Either value may be a success value (a Right) or a failure value (a Left).

ZIO 2: Solution to "ZIO.cond not working" (code not running)

I just wrote the following ZIO 2 question about how to use ZIO.cond to a friend, and get the answer shown. I’ve also added in my own comments where they make sense.

ZIO.done question

Hey, I’m trying to understand why the failWithMsgEffect doesn’t seem to get run in the following code example?

I have learned that there are better ways to handle this, but I’ve found that if I don’t understand something like this, it will come back to bite me later. Here’s the code:

ZIO 2: A ZIO.timeout interrupt example with ZIO.attempt

As a little ZIO 2 example with Scala 3, here’s some code that starts to show how to use ZIO.timeout along with ZIO.attempt while accessing an internet URL with Scala’s Source.fromURL.

Basically I attempt to access a URL using Scala’s Source.fromURL, and then I add a timeout to that, specifically a ZIO##timeout:

Scala: How to download URL contents to a String or file

Scala URL FAQ: How do I download the contents of a URL to a String or file in Scala?

I ran a few tests last night in the Scala REPL to see if I could think of different ways to download the contents of a URL to a String or file in Scala, and came up with a couple of different solutions, which I'll share here.

Download URL contents to a String in Scala

The best way I could think of to download the contents of a URL to a String looks like this:

Scala: How to square a number (Int, Double, Float, Long)

Scala math FAQ: How do I square a number in Scala, such as squaring an Int, Double, Long, or Float?


You can square a number in Scala in at least two different ways:

  1. Multiply the number by itself
  2. Call the Java Math.pow function or the scala.math.pow function

Scala and the two kinds of programming languages

I know that it’s fashionable to say that Scala is dead or something similar to that, but I’ve gotten a few royalty checks from O’Reilly this year for the Scala Cookbook that are amazingly good (💰) for a 3-year old programming book.

Shoot, I’d be happy to receive these royalty payments during the initial months after the book’s release.

As Bjarne Stroustrup said, “There are only two kinds of programming languages: the ones people complain about and the ones nobody uses.”