Programming Ecto Build database apps in Elixir for scalability and performance Darin Wilson
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Table of Contents
1 Foreword
2. A Vain Attempt at a Justification, Take Two
1. Acknowledgments
3 1. Take the Red Pill
1. Programming Should Be About Transforming Data
2 Installing Elixir
3. Running Elixir
4 Suggestions for Reading the Book
5. Exercises
6. Think Different(ly)
4 Part I. Conventional Programming
1. 2. Pattern Matching
1. Assignment: I Do Not Think It Means What You Think It Means.
2 More Complex Matches
3. Ignoring a Value with (Underscore)
4. Variables Bind Once (per Match)
5. Another Way of Looking at the Equals Sign
2. 3. Immutability
1 You Already Have (Some) Immutable Data
2. Immutable Data Is Known Data
3. Performance Implications of Immutability
4 Coding with Immutable Data
3. 4. Elixir Basics
1. Built-in Types
2 Value Types
3. System Types
4 Collection Types
5. Maps
6 Binaries
7. Dates and Times
8. Names, Source Files, Conventions, Operators, and So On
9. Variable Scope
10. End of the Basics
4 5. Anonymous Functions
1. Functions and Pattern Matching
2. One Function, Multiple Bodies
3. Functions Can Return Functions
4. Passing Functions as Arguments
5. Functions Are the Core
5. 6. Modules and Named Functions
1 Compiling a Module
2. The Function’s Body Is a Block
3. Function Calls and Pattern Matching
4. Guard Clauses
5. Default Parameters
6. Private Functions
7. The Amazing Pipe Operator: |>
8 Modules
9. Module Attributes
10 Module Names: Elixir, Erlang, and Atoms
11 Calling a Function in an Erlang Library
12. Finding Libraries
6. 7. Lists and Recursion
1 Heads and Tails
2. Using Head and Tail to Process a List
3 Using Head and Tail to Build a List
4. Creating a Map Function
5 Reducing a List to a Single Value
6. More Complex List Patterns
7. The List Module in Action
8. Get Friendly with Lists
7. 8. Maps, Keyword Lists, Sets, and Structs
1 How to Choose Between Maps, Structs, and Keyword Lists
2. Keyword Lists
3. Maps
4. Pattern Matching and Updating Maps
5. Updating a Map
6. Structs
7. Nested Dictionary Structures
8. Sets
9. With Great Power Comes Great Temptation
8. 9. An Aside—What Are Types?
9 10. Processing Collections—Enum and Stream
1. Enum Processing Collections
2 Streams Lazy Enumerables
3. The Collectable Protocol
4 Comprehensions
5. Moving Past Divinity
10. 11. Strings and Binaries
1. String Literals
2. The Name “strings”
3 Single-Quoted Strings Lists of Character Codes
4. Binaries
5 Double-Quoted Strings Are Binaries
6. Binaries and Pattern Matching
7 Familiar Yet Strange
11 12. Control Flow
1. if and unless
2 cond
3. case
4 Raising Exceptions
5. Designing with Exceptions
6. Doing More with Less
12
13. Organizing a Project
1. The Project: Fetch Issues from GitHub
2 Step 1: Use Mix to Create Our New Project
3. Transformation: Parse the Command Line
4 Write Some Basic Tests
5. Refactor: Big Function Alert
6. Transformation: Fetch from GitHub
7. Step 2: Use Libraries
8. Transformation: Convert Response
9. Transformation: Sort Data
10. Transformation: Take First n Items
11 Transformation: Format the Table
12. Step 3: Make a Command-Line Executable
13 Step 4: Add Some Logging
14 Step 5: Create Project Documentation
15. Coding by Transforming Data
13. 14. Tooling
1 Debugging with IEx
2. Testing
3 Code Dependencies
4. Server Monitoring
5 Source-Code Formatting
6. Inevitably, There’s More 5.
Part II. Concurrent Programming
1. 15. Working with Multiple Processes
1 A Simple Process
2. Process Overhead
3. When Processes Die
4. Parallel Map The “Hello, World” of Erlang
5. A Fibonacci Server
6. Agents A Teaser
7. Thinking in Processes
2. 16. Nodes—The Key to Distributing Services
1. Naming Nodes
2. Naming Your Processes
3. Input, Output, PIDs, and Nodes
4. Nodes Are the Basis of Distribution
3 17. OTP: Servers
1. Some OTP Definitions
2. An OTP Server
3. GenServer Callbacks
4 Naming a Process
5. Tidying Up the Interface
6. Making Our Server into a Component
4 18. OTP: Supervisors
1. Supervisors and Workers
2 Worker Restart Options
3. Supervisors Are the Heart of Reliability
5. 19. A More Complex Example
1. Introduction to Duper
2. The Duper Application
3 But Does It Work?
4. Planning Your Elixir Application
5 Next Up
6. 20. OTP: Applications
1. This Is Not Your Father’s Application
2. The Application Specification File
3. Turning Our Sequence Program into an OTP Application
4 Supervision Is the Basis of Reliability
5. Releasing Your Code
6 Distillery The Elixir Release Manager
7. OTP Is Big Unbelievably Big
7. 21. Tasks and Agents
1 Tasks
2. Agents
3 A Bigger Example
4. Agents and Tasks, or GenServer?
Part III. More Advanced Elixir
1. 22. Macros and Code Evaluation
1. Implementing an if Statement
2. Macros Inject Code
3 Using the Representation as Code
4. Using Bindings to Inject Values
5 Macros Are Hygienic
6. Other Ways to Run Code Fragments
7 Macros and Operators
8. Digging Deeper
9. Digging Ridiculously Deep
2 23. Linking Modules: Behavio(u)rs and use
1. Behaviours
2 use and using
3. Putting It Together Tracing Method Calls
4. Use use
3 24. Protocols—Polymorphic Functions
1. Defining a Protocol
2 Implementing a Protocol
3. The Available Types
4 Protocols and Structs
5. Built-in Protocols
6. Protocols Are Polymorphism
4 25. More Cool Stuff
1. Writing Your Own Sigils
2 Multi-app Umbrella Projects
3. But Wait! There’s More!
7. A1. Exceptions: raise and try, catch and throw
1. Raising an Exception
2 catch, exit, and throw
3. Defining Your Own Exceptions
4. Now Ignore This Appendix
8 A2. Type Specifications and Type Checking
1. When Specifications Are Used
2 Specifying a Type
3. Defining New Types
4 Specs for Functions and Callbacks
5. Using Dialyzer
9. Bibliography
Foreword
I have always been fascinated with how changes in hardware affect how we write software.
A couple of decades ago, memory was a very limited resource. It made sense back then for our software to take hold of some piece of memory and mutate it as necessary. However, allocating this memory and cleaning up after we no longer needed it was a very error-prone task. Some memory was never freed; sometimes memory was allocated over another structure, leading to faults. At the time, garbage collection was a known technique, but we needed faster CPUs in order to use it in our daily software and free ourselves from manual memory management. That has happened most of our languages are now garbage-collected.
Today, a similar phenomenon is happening. Our CPUs are not getting any faster. Instead, our computers get more and more cores. This means new software needs to use as many cores as it can if it is to maximize its use of the machine. This conflicts directly with how we currently write software.
In fact, mutating our memory state actually slows down our software when many cores are involved. If you have four cores trying to access and manipulate the same piece of memory, they can trip over each other. This potentially corrupts memory unless some kind of synchronization is applied.
I quickly learned that applying this synchronization is manual, error prone, and tiresome, and it hurts performance. I suddenly realized that’s not how I wanted to spend time writing software in the next years of my career, and I set out to study new languages and technologies.
It was on this quest that I fell in love with the Erlang virtual machine and ecosystem.
In the Erlang VM, all code runs in tiny concurrent processes, each with its own state. Processes talk to each other via messages. And since all communication happens by messagepassing, exchanging messages between different machines on the same network is handled transparently by the VM, making it a perfect environment for building distributed software!
However, I felt there was still a gap in the Erlang ecosystem. I missed first-class support for some of the features I find necessary in my daily work things such as metaprogramming, polymorphism, and first-class tooling. From this need, Elixir was born.
Elixir is a pragmatic approach to functional programming. It values its functional foundations and it focuses on developer productivity. Concurrency is the backbone of Elixir software. As garbage collection once freed developers from the shackles of memory management, Elixir is here to free you from antiquated concurrency mechanisms and bring you joy when writing concurrent code.
A functional programming language lets us think in terms of functions that transform data. This transformation never mutates data. Instead, each application of a function potentially creates a new, fresh version of the data. This greatly reduces the need for data-synchronization mechanisms.
Elixir also empowers developers by providing macros. Elixir code is nothing more than data, and therefore can be manipulated via macros like any other value in the language.
Finally, object-oriented programmers will find many of the mechanisms they consider essential to writing good software, such as polymorphism, in Elixir.
All this is powered by the Erlang VM, a 20-year-old virtual machine built from scratch to support robust, concurrent, and distributed software. Elixir and the Erlang VM are going to change how you write software and make you ready to tackle the upcoming years in programming.
I’m a language nut. I love trying languages out, and I love thinking about their design and implementation. (I know; it’s sad.)
I came across Ruby in 1998 because I was an avid reader of comp.lang.misc (ask your parents). I downloaded it, compiled it, and fell in love. As with any time you fall in love, it’s difficult to explain why. It just worked the way I work, and it had enough depth to keep me interested.
Fast-forward 15 years. All that time I’d been looking for something new that gave me the same feeling.
I came across Elixir a while back, but for some reason never got sucked in. But a few months before starting on the first edition of this book, I was chatting with Corey Haines. I was bemoaning the fact that I wanted a way to show people functional programming concepts without the academic trappings those books seem to attract. He told me to look again at Elixir. I did, and I felt the same way I felt when I first saw Ruby.
So now I’m dangerous. I want other people to see just how great this is. I want to evangelize. So I write a book. But I don’t want to write another 900-page Pickaxe book. I want this book to be short and exciting. So I’m not going into all the detail, listing all the syntax, all the library functions, all the OTP options, or….
Instead, I want to give you an idea of the power and beauty of this programming model. I want to inspire you to get involved, and then point to the online resources that will fill in the gaps.
But mostly, I want you to have fun.
Fast-forward three years. Elixir has moved on. Phoenix, its connectivity framework, introduced a whole new set of developers to the joys of a functional approach. The Nerves project makes it easy to write embedded Elixir code on Linuxbased microcontrollers. The Elixir base has grown there are international, national, and regional conferences. Job ads ask for Elixir developers.
I’ve been moving on, too. But I’m still using Elixir daily. I just completed my second year as an adjunct professor at Southern Methodist University, corrupting the programmers of tomorrow with the temptations of Elixir. I’ve written an online Elixir course.
[1]
And now I’m revving this book. To be honest, I don’t really have to: Elixir 1.6 is not so different from 1.3 that the older book would not be useful. But my own thinking about Elixir has matured. I now do some things differently. And I’d like to share these things with you.
Acknowledgments
It seems to be a common thread the languages I fall in love with are created by people who are both clever and extremely nice. José Valim, the creator of Elixir, takes both of these adjectives to a new level. I owe him a massive thank-you for giving me so much fun over the last 18 months. Along with him, the whole Elixir core team has done an amazing job of cranking out an entire ecosystem that feels way more mature than its years. Thank you, all.
A conversation with Corey Haines reignited my interest in Elixir thank you, Corey, for good evenings, some interesting times in Bangalore, and the inspiration.
Bruce Tate is always an interesting sounding board, and his comments on early drafts of the book made a big difference. And I’ve been blessed with an incredible number of active and insightful beta readers who have made literally hundreds of suggestions for improvements. Thank you, all.
A big tip of the hat to Jessica Kerr, Anthony Eden, and Chad Fowler for letting me steal their tweets.
Kim Shrier seems to have been involved with my writing since before I started writing. Thanks, Kim, for another set of perceptive and detailed critiques.
Candace Cunningham again amazed me with her detailed copy editing: it’s rare to find someone who can correct both your grammar and your code. The crew at Potomac did their customary stellar job of indexing.
The Elixir programming language wraps functional programming with immutable state and an actor-based approach to concurrency in a tidy, modern syntax. And it runs on the industrial-strength, high-performance, distributed Erlang VM. But what does all that mean?
It means you can stop worrying about many of the difficult things that currently consume your time. You no longer have to think too hard about protecting your data consistency in a multithreaded environment. You worry less about scaling your applications. And, most importantly, you can think about programming in a different way.
Programming Should Be About Transforming Data
If you come from an object-oriented world, then you are used to thinking in terms of classes and their instances. A class defines behavior, and objects hold state. Developers spend time coming up with intricate hierarchies of classes that try to model their problem, much as Victorian scientists created taxonomies of butterflies.
When we code with objects, we ’ re thinking about state. Much of our time is spent calling methods in objects and passing them other objects. Based on these calls, objects update their own state, and possibly the state of other objects. In this world, the class is king it defines what each instance can do, and it implicitly controls the state of the data its instances hold. Our goal is data-hiding.
But that’s not the real world. In the real world, we don’t want to model abstract hierarchies (because in reality there aren’t that many true hierarchies). We want to get things done, not maintain state.
Right now, for instance, I’m taking empty computer files and transforming them into files containing text. Soon I’ll transform those files into a format you can read. A web server somewhere will transform your request to download the book into an HTTP response containing the content.
I don’t want to hide data. I want to transform it.
COMBINE TRANSFORMATIONS WITH PIPELINES
Unix users are accustomed to the philosophy of small, focused command-line tools that can be combined in arbitrary ways. Each tool takes an input, transforms it, and writes the result in a format the next tool (or a human) can use.
This philosophy is incredibly flexible and leads to fantastic reuse. The Unix utilities can be combined in ways undreamed of by their authors. And each one multiplies the potential of the others.
It’s also highly reliable each small program does one thing well, which makes it easier to test.
There’s another benefit. A command pipeline can operate in parallel. If I write
$ grep Elixir *.pml | wc -l
the word-count program, wc, runs at the same time as the grep command. Because wc consumes grep ’ s output as it is produced, the answer is ready with virtually no delay once grep finishes.
Just to give you a taste of this, here’s an Elixir function called pmap. It takes a collection and a function, and returns the list that results from applying that function to each element of the collection. But…it runs a separate process to do the conversion of each element. Don’t worry about the details for now.
spawn/pmap1.exs
defmodule Parallel do def pmap(collection, func) do collection
|> Enum.map(&(Task.async(fn -> func.(&1) end)))
|> Enum.map(&Task.await/1) end end
We could run this function to get the squares of the numbers from 1 to 1,000.
result = Parallel pmap 1 1000, &(&1 * &1)
And, yes, I just kicked off 1,000 background processes, and I used all the cores and processors on my machine.
The code may not make much sense, but by about halfway through the book, you’ll be writing this kind of thing for yourself.
FUNCTIONS ARE DATA TRANSFORMERS
Elixir lets us solve the problem in the same way the Unix shell does. Rather than have command-line utilities, we have functions. And we can string them together as we please. The smaller more focused those functions, the more flexibility we have when combining them.
If we want, we can make these functions run in parallel Elixir has a simple but powerful mechanism for passing messages between them. And these are not your father’s boring old processes or threads we ’ re talking about the potential to run millions of them on a single machine and have hundreds of these machines interoperating. Bruce Tate commented on this paragraph with this thought: “Most programmers treat threads and processes as a necessary evil; Elixir developers feel they are an important simplification.” As we get deeper into the book, you’ll start to see what he means.
This idea of transformation lies at the heart of functional programming: a function transforms its inputs into its output. The trigonometric function sin is an example give it π/4, and you’ll get back 0.7071. An HTML templating system is a
function; it takes a template containing placeholders and a list of named values, and produces a completed HTML document.
But this power comes at a price. You’re going to have to unlearn a whole lot of what you know about programming. Many of your instincts will be wrong. And this will be frustrating, because you ’ re going to feel like a total n00b.
Personally, I feel that’s part of the fun. You didn’t learn, say, object-oriented programming overnight. You are unlikely to become a functional programming expert by breakfast, either.
But at some point things will click. You’ll start thinking about problems in a different way, and you’ll find yourself writing code that does amazing things with very little effort on your part. You’ll find yourself writing small chunks of code that can be used over and over, often in unexpected ways (just as wc and grep can be).
Your view of the world may even change a little as you stop thinking in terms of responsibilities and start thinking in terms of getting things done. And just about everyone can agree that will be fun.
Installing Elixir
This book assumes you ’ re using at least Elixir 1.6. The most upto-date instructions for installing Elixir are available at http://elixir-lang.org/install.html. Go install it now.
Running Elixir
In this book, I show a terminal session like this:
$ echo Hello, World Hello, World
The terminal prompt is the dollar sign, and the stuff you type follows. (On your system, the prompt will likely be different.) Output from the system is shown without highlighting.
IEX—INTERACTIVE ELIXIR
To test that your Elixir installation was successful, let’s start an interactive Elixir session. At your regular shell prompt, type iex.
Interactive Elixir (x.y.z) - press Ctrl+C to exit (type h() ENTER for h elp)
iex(1)>
(The various version numbers you see will likely be different I won’t bother to show them on subsequent examples.)
Once you have an IEx prompt, you can enter Elixir code and you’ll see the result. If you enter an expression that continues over more than one line, IEx will prompt for the additional lines with an ellipsis (…).
The number in the prompt increments for each complete expression executed. I’ll omit the number in most of the examples that follow.
There are several ways of exiting from IEx none are tidy. The easiest two are typing Ctrl - C twice or typing Ctrl - G followed by q and Return . On some systems, you can also use a single Ctrl - \ .
IEx Helpers
IEx has a number of helper functions. Type h (followed by Return ) to get a list:
iex> h
IEx Helpers
Welcome to Interactive Elixir. You are currently seeing the documentation for the module IEx.Helpers which provides many helpers to make Elixir's shell more joyful to work with.
This message was triggered by invoking the helper h(), usually referred to as h/0 (since it expects 0 arguments).
You can use the h/1 function to invoke the documentation for any Elixir module or function:
iex> h(Enum)
iex> h(Enum.map)
iex> h(Enum.reverse/1)
You can also use the i/1 function to introspect any value you have in the shell:
iex> i("hello")
There are many other helpers available, here are some examples:
• b/1 - prints callbacks info and docs for a given module
• c/1 - compiles a file into the current directory
• c/2 - compiles a file to the given path
• cd/1 - changes the current directory
• clear/0 - clears the screen
• exports/1 - shows all exports (functions + macros) in a module
• flush/0 - flushes all messages sent to the shell
• h/0 - prints this help message
• h/1 - prints help for the given module, function or macro
• i/0 - prints information about the last value
• i/1 - prints information about the given term
• ls/0 - lists the contents of the current directory
• ls/1 - lists the contents of the specified directory
• open/1 - opens the source for the given module or function in your editor
• pid/1 - creates a PID from a string
• pid/3 - creates a PID with the 3 integer arguments passed
• ref/1 - creates a Reference from a string
• ref/4 - creates a Reference with the 4 integer arguments passed
• pwd/0 - prints the current working directory
• r/1 - recompiles the given module's source file
• recompile/0 - recompiles the current project
• runtime info/0 - prints runtime info (versions, memory usage, stats)
• v/0 - retrieves the last value from the history
• v/1 - retrieves the nth value from the history
Help for all of those functions can be consulted directly from the command line using the h/1 helper itself. Try:
iex> h(v/0)
To list all IEx helpers available, which is effectively all exports (functions and macros) in the IEx.Helpers module:
iex> exports(IEx.Helpers)
This module also includes helpers for debugging purposes, see IEx break!/4 for more information.
To learn more about IEx as a whole, type h(IEx).
In the list of helper functions, the number following the slash is the number of arguments the helper expects.
Probably the most useful is h itself. With an argument, it gives you help on Elixir modules or individual functions in a module. This works for any modules loaded into IEx (so when we talk
Another random document with no related content on Scribd:
1.
October 1, 1811. Cavalry.
General Total, including serjeants, 58263 sabres and bayonets in the field
January 8, 1812.—Cavalry.
General Total, including sergeants, 56239 sabres and bayonets in the field.
Note The abuses and desertions in the Portuguese cavalry had been so great that one division was suppressed
5, 1812.—Cavalry.
Note. The heavy German cavalry were in the rear at Estremos, and two Portuguese regiments were in Abrantes
Hamilton’s division 4685
Light division 858
Third division 976
Fourth division 2384
Fifth division 1845 10748
Total 21,784 , 1812.
Cavalry under general Hill Left Wing
British 783
Portuguese 347 1130
Infantry ditto.
British 6156 Portuguese 2385 8541 Total under general Hill 9671
Cavalry under general Graham Right Wing
British 3517 Portuguese 3517
Infantry ditto.
British 10154 Portuguese 5896 16050
Total under general Graham 19567
General Total of the covering army, exclusive of the artillerymen and the heavy German cavalry, who remained in the rear at
Estremos, 29238 sabres and bayonets
2.
- , 1812.
.
Fourth division.
Fifth division.
FOOTNOTE:
[3] These regiments were attached by companies to the third, fourth, and fifth divisions.
Total Portuguese loss at the assault.
British loss during the whole siege. Officers. Sergeants. Soldiers. Total. 60 45 715 killed }
the whole siege.
Under arms. Detached. Absent. Effective.
Observation In September 1811 an army of reserve, consisting of two divisions of infantry and one of cavalry, with artillery, in all 20,287 under arms, was formed for the armée du midi.
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“The care bestowed upon this subject by Sir Hew Dalrymple is evident in the publication before us, which is unquestionably a most dignified, clear, and satisfactory vindication of Sir Hew’s motives and conduct, and forms, with the documents in the Appendix, a very valuable and authentic addition to the materials for the history of the period in question. Without a participation in the facts it discloses, the records of the war, as far as regards this particular subject, are, in fact, incomplete or distorted.”——United Service Journal.
“These volumes, the work of a gentleman of high and varied accomplishments, whose opportunities of observation have been unusually extensive and well-improved, will command and repay attention. They contain by far the best account of Spain which has yet issued from the press.”——United Service Gazette.
ADVENTURES IN THE RIFLE BRIGADE IN THE
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THE HISTORY OF THE
K I N G ’ S G E R M A N L E G I O N ,
FROM THE PERIOD OF ITS ORGANIZATION IN 1803, TO THAT OF ITS DISSOLUTION IN 1816.
Compiled from Manuscript Documents.
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LENT LECTURES.
I. On the Life of Christ. II. On the Life of St. Paul. III. On the Lord’s Prayer. IV. On the Liturgy of the Church of England.
V On the Creeds and Sacraments of the Church of England.
Preached in the Church of St. Mary, Bryanston Square, B REVEREND
T F DIBDIN, D D RECTOR
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T EXPECTATIONS FORMED ASSYRIANS, GREAT DELIVERER WOULD APPEAR, T L ’ A , . 8vo. price 10s. boards.
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MOMENTS OF IDLENESS;
A PEEP INTO THE WORLD WE CALL “OURS
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“Il y en a qui ne font rien,—il y en a d’autres qui font des riens.”
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WALTER;
OR,
A WORD MORE TO THE WISE
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Hunchback, Act 1. Scene 2.
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TRANSCRIBER’S NOTE
Footnote [3] has two anchors on page 587
Obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources.
Some hyphens in words have been silently removed, some added, when a predominant preference was found in the original book.
To save space in the wide tables in Note IX of the Appendix, the heading ‘Hospital.’ has been abbreviated to ‘Hosp.’.
In those sections of the Appendix that are French documents, some corrections to accents have been made silently; primarily é for e, and e for é. Incorrect grammar and spelling have been left unchanged.
Except for those changes noted below, all misspellings in the text, and inconsistent or archaic usage, have been retained.
Table of Contents:
Pg iii: ‘on the Orbigo’ replaced by ‘on the Orvigo’.
Pg iii: ‘General Leval’ replaced by ‘General Laval’.
Pg v: ‘the mili ary force’ replaced by ‘the military force’.
Main text:
Pg 5: ‘by sea to St. Ander’ replaced by ‘by sea to Santander’.
Pg 13: ‘he surprized some’ replaced by ‘he surprised some’.
Pg 33: ‘embarrasments thus’ replaced by ‘embarrassments thus’.
Pg 48: ‘and Legre rivers’ replaced by ‘and Segre rivers’.
Pg 51: ‘to war down’ replaced by ‘to wear down’.
Pg 61: ‘Promothean touch’ replaced by ‘Promethean touch’.
Pg 135: ‘commucating with the alledged’ replaced by ‘communicating with the alleged’.
Pg 141: ‘were they all’ replaced by ‘where they all’.
Pg 162: ‘the admistration’ replaced by ‘the administration’.
Pg 164: ‘Mr. Suart and’ replaced by ‘Mr. Stuart and’.
Pg 169: ‘acknowleged that’ replaced by ‘acknowledged that’.
Pg 169: ‘a proponderance to’ replaced by ‘a preponderance to’.
Pg 170: ‘Rio Janeiro’ replaced by ‘Rio de Janeiro’.
Pg 196: ‘aid-du-camp’ replaced by ‘aide-de-camp’.
Pg 231: ‘Miunte reports of’ replaced by ‘Minute reports of’.
Pg 243: ‘Aldea Ponte’ replaced by ‘Aldea de Ponte’.
Pg 245: ‘behind the Soita’ replaced by ‘behind Soita’.
Pg 268: ‘which caanot now’ replaced by ‘which cannot now’.
Pg 296, image caption: ‘The Seige’ replaced by ‘The Siege’.
Pg 309: ‘also an artifical’ replaced by ‘also an artificial’.
Pg 310: ‘and Catalayud to’ replaced by ‘and Calatayud to’.
Pg 314: ‘were straightened’ replaced by ‘were straitened’.
Pg 319: ‘a confidental’ replaced by ‘a confidential’.
Pg 319: ‘the Guadalquiver’ replaced by ‘the Guadalquivir’.
