What is a monad in Scala? alvin August 15, 2019 - 11:07am

I started to write about what a monad is in Scala, but then I realized I’ve already done that in several places, including my tutorial, What do effect and effectful mean in functional programming. Therefore, I encourage you to read that article for more details, but as a brief introduction, here’s part of what I wrote there:

Scala: What do “effect” and “effectful” mean in functional programming?

When you get started with functional programming (FP) a common question you’ll have is, “What is an effect in functional programming?” You’ll hear advanced FPers use the words effects and effectful, but it can be hard to find a definition of what these terms mean.

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

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. For reasons I don’t remember, I decided not to include it in the book, and forgot about it until I recently started using GraalVM (what I call Graal).

Graal includes a native image feature lets you compile JVM classes and JAR files into native executables, so as I thought about things I can make faster, I was reminded of the To-Do List app and thought about how cool it would be if it started instantaneously. So I found the old project, blew the dust off of it (updated all of its dependencies), and made a few additions so I could create (a) a single, executable JAR file with sbt-assembly, and (b) a native executable with Graal.

Scala: “IO monad doesn’t make a function pure; it just makes it obvious it’s impure” alvin July 21, 2018 - 11:15am

I always find it confusing when people claim that the IO monad somehow makes an impure function pure. Frankly, I think that argument does a confusing disservice to people who are trying to learn functional programming (FP).

Why Haskell has monads

“If it wasn’t for the problem of how to sequence input-output actions correctly, monads probably wouldn’t have appeared in Haskell. But once it was appreciated what they could do, all kinds of other uses quickly followed.”

~ Thinking Functionally with Haskell, Richard Bird

Scala: Handling nested Options with flatMap and for

Summary: In this article I show a couple of ways to extract information from optional fields in your Scala domain models. This example is a little contrived, but if you have a situation where one Option instance contains one or more other Options, this article may be helpful.

There are times when you’re creating your domain model when it makes sense to use optional fields in your case classes. For instance, when you model an Address, the “second street address” isn’t needed for all people, so making it an optional field makes sense:

Scala 2.12: Either is biased, implements map and flatMap

While reading the excellent Scala/FP book, Advanced Scala with Cats, I was just reminded that Scala’s Either class was redesigned in Scala 2.12. Prior to 2.12, Either was not biased, and didn’t implement map and flatMap methods. As the image from the book shows, Either is redesigned in 2.12 to include those methods, so it can now be used in Scala for-expressions as shown.

(I write about biasing in my book, Learning Functional Programming in Scala.)