match

A Scala shell script to insert text before a matching pattern

I don’t remember exactly why I wrote this Scala shell script, but if I remember right I was having a problem getting sed to work properly, so I wrote this little script to insert an Amazon Kindle “break” tag before each <h1> tag in an HTML file:

Scala: How to extract parts of a String that match regex patterns

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.9, “Extracting Parts of a String that Match Patterns.”

Problem

You want to extract one or more parts of a Scala String that match the regular-expression patterns you specify.

Solution

Define the regular-expression (regex) patterns you want to extract, placing parentheses around them so you can extract them as “regular-expression groups.” First, define the desired pattern:

How to find regex patterns in Scala strings

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.7, “Finding Patterns in Scala Strings.”

Problem

You need to determine whether a Scala String contains a regular expression pattern.

Recursion: How to Write a ‘sum’ Function in Scala alvin May 29, 2017 - 10:49am

With all of the images of the previous lesson firmly ingrained in your brain, let’s write a sum function using recursion!

Sketching the sum function signature

Given a List of integers, such as this one:

val list = List(1, 2, 3, 4)

let’s start tackling the problem in the usual way, by thinking, “Write the function signature first.”

Scala best practice: How to use the Option/Some/None pattern

Table of Contents1 - Problem2 - Solution3 - Returning an Option from a method4 - Getting the value from an Option5 - Using Option with Scala collections6 - Using Option with other frameworks7 - Using Try, Success, and Failure8 - Using Either, Left, and Right9 - Discussion10 - Don’t use the get method with Option11 - See Also12 - The Scala Cookbook

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 20.6, “Scala best practice: How to use the Option/Some/None pattern.”

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Problem

For a variety of reasons, including removing null values from your Scala code, you want to use what I call the Option/Some/None pattern. Or, if you’re interested in a problem (exception) that occurred while processing code, you may want to return Try/Success/Failure from a method instead of Option/Some/None.

How to use multiple regex patterns with replaceAll (Java String class)

Table of Contents1 - 1) A simple string2 - 2) Replace multiple patterns in that string3 - 3) More explanation4 - Multiple search patterns5 - Summary

Java FAQ: How can I use multiple regular expression patterns with the replaceAll method in the Java String class?

Here’s a little example that shows how to replace many regular expression (regex) patterns with one replacement string in Scala and Java. I’ll show all of this code in Scala’s interactive interpreter environment, but in this case Scala is very similar to Java, so the initial solution can easily be converted to Java.

How to create and use partial functions in Scala

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 9.8, “How to create and use partial functions in Scala.”

Problem

You want to define a function that will only work for a subset of possible input values, or you want to define a series of functions that only work for a subset of input values, and combine those functions to completely solve a problem.

How to match one or more exceptions with try/catch in Scala

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 3.16, “How to match one or more exceptions with try/catch in Scala.”

Problem

You want to catch one or more exceptions in a try/catch block.

Solution

The Scala try/catch/finally syntax is similar to Java, but it uses the match expression approach in the catch block:

How to use Lists in Scala match expressions alvin June 7, 2015 - 3:57pm

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 3.15, “How to use Lists in Scala match expressions.”

Problem

You know that a List data structure is a little different than other collection data structures. It’s built from “cons” cells and ends in a Nil element. You want to use this to your advantage when working with a match expression, such as when writing a recursive function.