Hands-on Scala Programming

This repository is the online hub for the book Hands-on Scala Programming:

• Chapter Notes, Errata, and Discussion: go here if you want to leave comments or ask questions about individual chapters

• Code Snippets: copy-paste friendly versions of every code snippet in the book

• Chapter Resource Files: files used as part of the book's programming exercises

• Executable Code Examples: self-contained executable programs for the topics being presented in each chapter.

Executable Code Examples

The executable code examples from Hands-on Scala are freely available online, and open source under an MIT license. Each example is:

• Self-contained: to be run either using the Ammonite script runner or Mill build tool, with no other setup

• Tested: with simple test suites provided and instructions on how to run each example in that folder's readme.md file

• Executable: you can download the folder and run the example yourself to see it in action

Many of the examples are related, with only small code changes between them to illustrate a new feature or technique. The readme.md file of such downstream examples will show a diff from the upstream example that it was based upon, so you can focus your attention on the important code changes that are happening, with a link back up to the upstream example.

The executable code examples below are organized by each part and each chapter of the book.

Part I Introduction to Scala

Chapter 1: Hands-on Scala

Chapter 2: Setting Up

Chapter 3: Basic Scala

Chapter 4: Scala Collections

Chapter 5: Notable Scala Features

Part II Local Development

Chapter 6: Implementing Algorithms in Scala

• 6.1 - MergeSort: Simple merge-sort implemention, hard-coded to only work on Array[Int]
• 6.2 - GenericMergeSort: Generic merge sort implemention, that can sort any IndexedSeq[T] with an Ordering
• 6.3 - Trie: A simple mutable Trie implemention
• 6.4 - Search: Breadth-first-search implemention
• 6.5 - SearchPaths: Breadth-first-search implemention that keeps track of the shortest paths to every node
• 6.6 - BinarySearch: Binary search implementation
• 6.7 - ImmutableTrie: Immutable trie implementation
• 6.8 - DepthSearchPaths: Depth-first search implementation that keeps track of shortest paths

Chapter 7: Files and Subprocesses

• 7.1 - LargestFiles: Script to finds the largest 5 files in the current folder tree
• 7.2 - FileSync: Method to batch synchronize files between two local folders
• 7.3 - RemoveBranches: Script to remove all non-active branches from the local Git repository
• 7.4 - InteractivePython: Example of how to interact with a running Python process from Scala
• 7.5 - StreamingDownloadProcessReupload1: Three-stage streaming subprocess pipeline
• 7.6 - StreamingDownloadProcessReupload2: Four-stage streaming subprocess pipeline
• 7.7 - FileSyncDelete: Method to synchronize files between two folders, with support for deletion
• 7.8 - StreamingDownloadProcessReuploadTee: Five stage subprocess pipeline, teed streaming data to a file

Chapter 8: JSON and Binary Data Serialization

• 8.1 - Create: Parsing JSON structures from strings and constructing it directly
• 8.2 - Manipulate: Querying and modifying JSON structures in-memory
• 8.3 - Traverse: Recursively traversing a JSON structure
• 8.4 - SerializationBuiltins: Serializing built-in Scala data types to JSON
• 8.5 - SerializationCaseClass: Serializing Scala case classes to JSON
• 8.6 - SerializationBinary: Serializing Scala data types to binary MessagePack blobs
• 8.7 - BiMapClass: Using bimap to make a non-case class serializable

Chapter 9: Self-Contained Scala Scripts

• 9.1 - Printing: Listing blog-post-like files in a folder and printing them out
• 9.2 - Index: Rendering an index.html for our static blog using Scalatags
• 9.3 - Markdown: Rendering individual blog posts using Atlassian's Commonmark-Java library
• 9.4 - Links: Adding links between our index.html and the individual blog posts
• 9.5 - Bootstrap: Prettifying our static blog using the Bootstrap CSS framework
• 9.6 - Deploy: Optionally deploying our static blog to a Git repository
• 9.7 - DeployTimestamp: Displaying the .md file last-modified time on each blog post

Chapter 10: Static Build Pipelines

• 10.1 - Simple: Simple linear build pipeline
• 10.2 - Nonlinear: Simple non-linear build pipeline with two branches
• 10.3 - Modules: Simple non-linear build pipeline, replicated in several modules
• 10.4 - NestedModules: Nested modules in a Mill build pipeline
• 10.5 - CrossModules: Using cross-modules to dynamically construct a build graph based on the filesystem
• 10.6 - Blog: Our static blog generator, converted into an incremental Mill build pipeline
• 10.7 - ExtendedBlog: Adding previews and bundled Bootstrap CSS to our static blog build pipeline
• 10.8 - Push: Re-adding the ability to deploy our static blog by defining a T.command

Part III Web Services

Chapter 11: Scraping Websites

• 11.1 - ScrapingWiki: Scraping headlines off the Wikipedia front page using Jsoup
• 11.2 - ScrapingDocs: Scraping semi-structured content off of the Mozilla Development Network Web API docs
• 11.3 - ApiStatus: Using Jsoup to scrape the status annotations for every Web API on MDN
• 11.4 - ExternalLinks: Crawling the pages of a static website to extract every external link on the site

Chapter 12: Working with HTTP APIs

• 12.1 - IssueMigrator: Simple Github issue migrator
• 12.2 - IssueMigratorLink: Github issue migrator that adds a link back from every new issue to the original issue
• 12.3 - IssueMigratorClosed: Github issue migrator that also preserves issue open/closed status during the migration

Chapter 13: Fork-Join Parallelism with Futures

• 13.1 - Hashing: Hashing files in parallel using Futures
• 13.2 - Crawler: Simple sequential wikipedia crawler
• 13.3 - ParallelCrawler: Simple batch-by-batch parallel wikipedia crawler, using Futures and Requests-Scala
• 13.4 - RecursiveCrawler: Parallel wikipedia crawler written in a recursive fashion
• 13.5 - AsyncCrawler: Asynchronous parallel wikipedia crawler, using the Java AsyncHttpClient
• 13.6 - ParallelScrapingDocs: Scraping MDN Web API documentation pages in parallel using Futures
• 13.7 - ParallelMergeSort: Merge-sort implementation parallelized using Futures
• 13.8 - AsyncCrawlerThrottled: Asynchronous wikipedia crawler which limits the number of open requests
• 13.9 - AsyncThottledScrapingDocs: Asynchronous parallel MDN scraper that limits the number of open requests

Chapter 14: Simple Web and API Servers

• 14.1 - Mock: Dummy non-interactive HTML chat website and server
• 14.2 - Forms: Form-based interactive chat website
• 14.3 - Ajax: Ajax-based interactive chat website
• 14.4 - Websockets: Websocket-based real-time chat website
• 14.5 - WebsocketsFilter: Websocket-based chat website with ability to filter chats
• 14.6 - WebsocketsSynchronized: Websocket-based chat website with shared mutable state properly synchronized
• 14.7 - WebsocketsJsoup: Websocket-based chat website with HTML validation tests using Jsoup

Chapter 15: Querying SQL Databases

• 15.1 - Queries: Simple Quill database queries
• 15.2 - Website: Database-backed websocket chat website
• 15.3 - FancyQueries: Fancier Quill database queries with groupBy and sortBy
• 15.4 - WebsiteTimestamps: Database-backed websocket chat website with timestamps on every chat message

Part IV Program Design

Chapter 16: Message-based Parallelism with Actors

• 16.1 - Simple: Simple logging actor that asynchronously uploads log messages to httpbin.org servers
• 16.2 - Batch: Batch logging actor that uploads batches of log messages to httpbin.org servers
• 16.3 - StateMachine: Actor that uploads batches of logs to httpbin.org, with a minimum interval between each batch
• 16.4 - LoggingSimple: Logging actor that asynchronously logs messages to disk
• 16.5 - LoggingPipeline: Two-stage logging actor pipeline that asynchronously logs base64-encoded messages to disk
• 16.6 - LoggingLongPipeline: Four-actor pipeline that logs sanitized, base64-encoded messages both to disk and to httpbin.org
• 16.7 - LoggingRearrangedPipeline1: Three-actor logging pipeline without sanitization
• 16.8 - LoggingRearrangedPipeline2: Four-actor pipeline, with only disk logs base64-encoded and only httpbin.org uploads sanitized
• 16.9 - WebCrawler: A concurrent actor-based web crawler that avoids the limitations of earlier batch-by-batch crawlers
• 16.10 - WebCrawlerPipeline: A concurrent actor-based web crawler that streams the crawled pages to disk
• 16.11 - WebCrawlerThrottled: A concurrent actor-based web crawler that limits the number of open connections

Chapter 17: Multi-Process Applications

• 17.1 - FileSyncer: Simple two-process batch file synchronizer that could work over a network
• 17.2 - Pipelined: Pipelined version of our two-process file synchronizer, minimizing the chattiness of the protocol
• 17.3 - Deletes: Pipelined two-process file synchronizer that supports deletions

Chapter 18: Building a Real-time File Synchronizer

• 18.1 - Simple: Simple real-time file synchronizer that uses os.watch to react to filesystem changes as they happen
• 18.2 - Pipelined: Pipelined real-time file synchronizer, allowing RPCs and hashing to take place in parallel
• 18.3 - InitialFiles: Real-time file synchronizer that supports syncing an initial set of files
• 18.4 - ForkJoinHashing: Real-time file synchronizer that does hashing of files in parallel

Chapter 19: Parsing Structured Text

• 19.1 - Phrases: Parser for simple "hello world"-like phrases
• 19.2 - Arithmetic: Parser and evaluator for simple english-like arithmetic expressions
• 19.3 - ArithmeticChained: English-like arithmetic parser, allowing more than one binary operator to be chained together
• 19.4 - ArithmeticPrecedence: English-like arithmetic parser, supporting operator precedence of chained binary operators
• 19.5 - ArithmeticDirect: English-like arithmetic parser that evaluates the arithmetic without constructing a syntax tree

Chapter 20: Implementing a Programming Language

• 20.1 - Jsonnet: Interpreter for a minimal subset of the Jsonnet programming language
• 20.2 - JsonnetNumbers: Jsonnet interpreter with added support for simple integer arithmetic
• 20.3 - JsonnetPrettyPrinting: Jsonnet interpreter using the uJson library for pretty-printing the output JSON