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Scala Programming Projects

You're reading from   Scala Programming Projects Build real-world projects using popular Scala frameworks such as Play, Akka, and Spark

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Product type Paperback
Published in Sep 2018
Publisher Packt
ISBN-13 9781788397643
Length 398 pages
Edition 1st Edition
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Authors (2):
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Mikael Valot Mikael Valot
Author Profile Icon Mikael Valot
Mikael Valot
Nicolas Jorand Nicolas Jorand
Author Profile Icon Nicolas Jorand
Nicolas Jorand
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Toc

Table of Contents (13) Chapters Close

Preface 1. Writing Your First Program FREE CHAPTER 2. Developing a Retirement Calculator 3. Handling Errors 4. Advanced Features 5. Type Classes 6. Online Shopping - Persistence 7. Online Shopping - REST API 8. Online Shopping - User Interface 9. Interactive Browser 10. Fetching and Persisting Bitcoin Market Data 11. Batch and Streaming Analytics 12. Other Books You May Enjoy

Using ValidatedNel

In this chapter, we have seen how we can model the possibility of an optional value with Option and the possibility of an error with Either. We demonstrated how these types can replace exceptions while guaranteeing referential transparency.

We also saw how we can combine several Option or Either types using flatMap. This works well when we have to check for optional values or errors sequentially—call function1; if there is no error, call function2; if there is no error, call function3. If any of these functions return an error, we return that error and stop the call chain, as shown in the following code:

def sequentialErrorHandling(x: String): Either[MyError, String] =
for {
a <- function1(x)
b <- function2(a)
c <- function3(b)
} yield c

However, in some situations, we would want to call several functions in parallel and return...

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