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Scala: Examples of for-expressions being converted to map and flatMap

Without any explanation, here are a couple of source code examples from my book, Learning Functional Programming in Scala. The only thing I’ll say about this code is that I created it in the process of writing that book, and the examples show how the Scala compiler translates for-expressions into map and flatMap calls behind the scenes.

Example: How to use javapackager to build a MacOS application bundle

Table of Contents1 - Building a MacOS application bundle with javapackager2 - The longer story3 - The Mac/Java class4 - The three scripts5 - javapackager notes

I recently learned how to use the Java javapackager command to build a macOS application bundle — i.e., a regular macOS application — from a Java application. In this tutorial I’ll show how to create a Mac application bundle from a simple Java class, in this case a Java Swing class.

How to start a Scala REPL session inside SBT (Simple Build Tool)

Scala FAQ: How do I start a Scala REPL session from SBT (i.e., inside the Simple Build Tool)?

Answer: Use the console or consoleQuick commands inside the SBT shell:

  • Type console to start a REPL session from inside SBT. This (a) compiles your Scala project and then (b) starts a REPL session.
  • Type consoleQuick if you don’t want to compile your project before starting a REPL session inside of SBT.

The console command process looks like this:

> sbt
[info] Loading project definition from /Users/al/Projects/Cats101/project
[info] Set current project to Cats101 (in build file:/Users/al/Projects/Cats101/)

> console
[info] Starting scala interpreter...
[info]
Welcome to Scala 2.12.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_131).
Type in expressions for evaluation. Or try :help.

scala> _

If you wanted to see how to start a Scala REPL session from inside SBT, I hope this helps.

How curried functions and partially-applied functions compile in Scala

This morning I was curious about how Scala curried functions and partially-applied functions are really compiled at a bytecode level. Earlier this morning I made this post that Higher order functions are the Haskell experience — which is also implicitly about curried functions — and it got me thinking about Scala, in particular why we might use one function syntax versus another, i.e., why would I use this syntax:

How to compile, run, and package a Scala project with SBT

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 18.2, “How to compile, run, and package a Scala project with SBT.”

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Problem

You want to use SBT to compile and run a Scala project, and package the project as a JAR file.

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Solution

Create a directory layout to match what SBT expects, then run sbt compile to compile your project, sbt run to run your project, and sbt package to package your project as a JAR file.

Table of Contents

  1. Problem
  2. Solution
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How to make your Scala shell scripts run faster by pre-compiling them

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is a short recipe, Recipe 14.13, “How to make your Scala shell scripts run faster by pre-compiling them.”

Problem

You love using Scala as a scripting language, but you’d like to eliminate the lag time in starting up a script.

Solution

Use the -savecompiled argument of the Scala interpreter to save a compiled version of your script.

A basic Scala script like this:

How to compile Scala code faster with the 'fsc' command-line compiler

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is a short recipe, Recipe 14.9, “How to compile your Scala code faster with the 'fsc' command-line compiler.”

Problem

You’re making changes to a project and recompiling it with scalac, and you’d like to reduce the compile time.

Solution

Use the fsc command instead of scalac to compile your code:

How to compile Scala code with ‘scalac’ and run it with ‘scala’

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 14.5, “How to compile Scala code with 'scalac' and run it with 'scala'.”

Problem

Though you normally use the Simple Build Tool (SBT) to build Scala applications, you may want to use more basic tools to compile and run small test programs, in the same way you might use javac and java with small Java applications.