Download Free Books for iPad 2: Programming Elm by James Moore

# Free books download for ipad 2 Programming Elm: A beginner's guide

## Introduction

Welcome to this article on free books download for ipad 2 Programming Elm. If you are looking for a way to learn Elm, a modern functional programming language for web development, you have come to the right place. In this article, you will learn: - What is Elm and why should you learn it? - What are the benefits of Elm for web development? - How to install Elm and set up your development environment - Basic concepts of Elm - Building a simple web app with Elm - Advanced topics in Elm By the end of this article, you will have a solid understanding of Elm and how to use it to create beautiful and reliable web apps. You will also get access to some free books that you can download for your ipad 2 to learn more about Elm. So, let's get started!

### What is Elm and why should you learn it?

Elm is a functional programming language that compiles to JavaScript. It was created by Evan Czaplicki in 2012 as his thesis project at Harvard University. Since then, it has grown into a popular and mature language that is used by many companies and developers around the world. Elm is designed to make web development fun and easy. It has a simple and elegant syntax that is easy to read and write. It has a powerful type system that catches errors at compile time and prevents runtime exceptions. It has a built-in toolchain that handles everything from code formatting to testing to deployment. But what makes Elm really stand out is its architecture. Elm follows the Model-View-Update (MVU) pattern, which is a variation of the Model-View-Controller (MVC) pattern. In MVU, you have three components: - Model: This is where you store your application state. - View: This is where you define how your application looks like. - Update: This is where you define how your application responds to user input and events. The MVU pattern makes your code easy to understand and maintain. It also enables some amazing features, such as hot reloading, time travel debugging, and automatic code optimization. If you are familiar with React or Redux, you might notice some similarities between them and Elm. In fact, Elm was one of the inspirations for React and Redux. However, Elm goes beyond them by providing a complete solution for web development that does not require any external libraries or frameworks. Elm is not only a great language for beginners, but also for experienced developers who want to level up their skills and productivity. Learning Elm will teach you how to think in terms of functions, types, and data flows. It will also expose you to some advanced concepts, such as algebraic data types, pattern matching, and immutability. Elm is a language that you will enjoy learning and using. It will make you a better web developer and a happier person.

### What are the benefits of Elm for web development?

Elm has many benefits for web development. Here are some of the most important ones: - No runtime errors: Elm guarantees that your code will not crash or throw exceptions at runtime. This is possible because Elm has a strong and static type system that checks your code for errors at compile time. If your code compiles, it works. This means that you can write code with confidence and avoid wasting time on debugging and fixing bugs. - Fast and reliable performance: Elm generates JavaScript code that is fast and efficient. Elm also optimizes your code for performance by using techniques such as dead code elimination, tree shaking, and minification. Elm also ensures that your code is reliable by using immutable data structures and pure functions. This means that your code will not have any side effects or unexpected behaviors that can affect the performance or correctness of your app. - Great developer experience: Elm has a great developer experience that makes web development fun and easy. Elm has a friendly and helpful compiler that gives you clear and helpful error messages and suggestions. Elm has a built-in toolchain that handles everything from code formatting to testing to deployment. Elm has a live reloading feature that updates your app in the browser as you save your code. Elm has a time travel debugger that lets you rewind and replay your app's history. Elm has a vibrant and supportive community that provides you with resources, tutorials, and help. - Beautiful and expressive syntax: Elm has a beautiful and expressive syntax that is easy to read and write. Elm has a minimal and consistent syntax that avoids unnecessary symbols and keywords. Elm has a concise and elegant syntax that lets you write more with less. Elm has a readable and meaningful syntax that makes your code self-documenting.

### How to install Elm and set up your development environment

To start using Elm, you need to install it on your computer and set up your development environment. Here are the steps to do so: - Install Elm: To install Elm, you need to download the installer from the official website: https://elm-lang.org/. The installer will guide you through the installation process and set up the necessary tools for you. Alternatively, you can use a package manager such as npm or Homebrew to install Elm. - Install an editor: To write Elm code, you need an editor that supports Elm syntax highlighting, auto-completion, formatting, and error checking. Some of the popular editors that support Elm are VS Code, Atom, Sublime Text, Emacs, and Vim. You can also use an online editor such as Ellie or Repl.it to try out Elm without installing anything. - Create a project: To create a project in Elm, you need to use the elm init command in your terminal. This will create a folder with the name of your project and some files inside it. The most important file is elm.json, which contains the configuration and dependencies of your project. - Run your project: To run your project in Elm, you need to use the elm reactor command in your terminal. This will start a local server that serves your project files on http://localhost:8000/. You can then open this URL in your browser and see your app running. That's it! You have successfully installed Elm and set up your development environment. You are now ready to write some Elm code.

## Basic concepts of Elm

Before we dive into building a web app with Elm, let's review some of the basic concepts of Elm that you need to know.

### The Elm architecture

The Elm architecture is the core pattern that defines how an Elm app works. It consists of three components: Model, View, and Update. - Model: The model is where you store your application state. It is usually defined as a record type that contains all the data that your app needs. - View: The view is where you define how your application looks like. It is usually defined as a function that takes the model as an argument and returns an HTML representation of it. - Update: The update is where you define how your application responds to user input and events. It is usually defined as a function that takes a message (an event) and the model as arguments and returns a new model. The flow of data in the Elm architecture is as follows:

clicks a button or types something in a field). 2. The view sends a message to the update function (e.g., ButtonClicked or TextInputChanged). 3. The update function receives the message and the current model and returns a new model based on the message (e.g., incrementing a counter or updating a text field). 4. The new model is passed to the view function, which renders a new HTML representation of it. 5. The cycle repeats. This way, your app is always in sync with your model and your view. You don't have to worry about manipulating the DOM or managing state manually. Elm handles everything for you. Here is an example of how the Elm architecture looks like in code: ```elm -- Define the model type alias Model = counter : Int , text : String -- Define the initial model init : Model init = counter = 0 , text = "" -- Define the messages type Msg = Increment Decrement ChangeText String -- Define the update function update : Msg -> Model -> Model update msg model = case msg of Increment ->

counter = model.counter + 1 Decrement ->

model ChangeText newText ->

text = newText -- Define the view function view : Model -> Html Msg view model = div [] [ h1 [] [ text "Elm Architecture Example" ] , p [] [ text "Counter: " ++ String.fromInt model.counter ] , button [ onClick Increment ] [ text "+" ] , button [ onClick Decrement ] [ text "-" ] , p [] [ text "Text: " ++ model.text ] , input [ onInput ChangeText ] [] ] -- Run the app main : Program () Model Msg main = Browser.sandbox init = init , view = view , update = update ``` You can try this code online here: https://ellie-app.com/fpZwLJ9Q7XBa1

### Data types and functions

Elm is a strongly typed language, which means that every value has a specific type and every expression has a type signature. Elm has some built-in types, such as Int, Float, String, Bool, List, and Tuple. You can also define your own types using type aliases and custom types. A type alias is a way to give a name to an existing type. For example, you can define a type alias for a record type that represents a person: ```elm type alias Person = name : String , age : Int ``` A custom type is a way to define a new type that can have multiple variants. For example, you can define a custom type for a shape that can be either a circle or a rectangle: ```elm type Shape = Circle Float -- radius Rectangle Float Float -- width and height ``` A function is a way to define a computation that takes some inputs and returns an output. For example, you can define a function that calculates the area of a shape: ```elm area : Shape -> Float area shape = case shape of Circle r ->

pi * r ^ 2 Rectangle w h ->

w * h ``` The first line of the function definition is the type signature, which tells you what type of inputs and output the function expects and returns. The second line is the function name and the parameter name. The rest of the lines are the function body, which contains an expression that returns the output. You can call a function by applying it to an argument or multiple arguments separated by spaces. For example, you can call the area function with a circle or a rectangle: ```elm area (Circle 5) -- returns 78.53981633974483 area (Rectangle 10 20) -- returns 200 ``` You can also define anonymous functions using the backslash (\) syntax. For example, you can define an anonymous function that doubles its input: ```elm \x -> x * 2 -- anonymous function (\x -> x * 2) 3 -- returns 6 List.map (\x -> x * 2) [1,2,3] -- returns [2,4,6] ``` You can also use the pipe (>) operator to pass the output of one function as the input of another function. For example, you can use the pipe operator to compose multiple functions: ```elm String.toUpper "hello" -- returns "HELLO" String.reverse "hello" -- returns "olleh" String.toUpper > String.reverse "hello" -- returns "OLLEH" ``` The pipe operator is useful for making your code more readable and expressive.

### Modules and packages

A module is a way to organize your code into separate files. Each file in your project is a module that has a name that matches its file name. For example, if you have a file called Main.elm, it is a module called Main. A module can expose some or all of its values (types, functions, etc.) to other modules using the expose keyword. For example, you can expose the area function from the previous section in a module called Shape.elm: ```elm module Shape exposing (Shape(..), area) type Shape = Circle Float Rectangle Float Float area : Shape -> Float area shape = -- same as before ``` The exposing keyword tells Elm which values are available to other modules. In this case, we are exposing the Shape type and its variants (Circle and Rectangle) and the area function. A module can also import some or all of the values from another module using the import keyword. For example, you can import the Shape module in another module called Main.elm: ```elm module Main exposing (main) import Shape exposing (Shape(..)) main : Shape main = Circle 10 ``` The import keyword tells Elm which module to import from. The exposing keyword tells Elm which values to import from that module. In this case, we are importing the Shape type and its variants from the Shape module. You can also use a dot (.) notation to access the values from a module without importing them. For example, you can access the area function from the Shape module like this: ```elm module Main exposing (main) import Shape main : Float main = Shape.area (Shape.Circle 10) ``` In this case, we are importing the whole Shape module, but we are not exposing any of its values. We can still access them using the dot notation. A package is a way to share your code with other developers. A package is a collection of modules that have a name, a version, and some dependencies. You can publish your package on the official Elm package website: https://package.elm-lang.org/. You can also use other people's packages in your project by adding them to your elm.json file. For example, you can use the elm/http package to make HTTP requests in your app: ```json "type": "application", "source-directories": [ "src" ], "elm-version": "0.19.1", "dependencies": "direct": "elm/browser": "1.0.2", "elm/core": "1.0.5", "elm/http": "2.0.0" , "indirect": ... , ... ``` You can then import and use the elm/http package in your modules: ```elm module Main exposing (main) import Browser import Http type alias User = id : Int , name : String , email : String type Msg = GotUser (Result Http.Error User) getUser : Int -> Cmd Msg getUser id = Http.get url = "https://jsonplaceholder.typicode.com/users/" ++ String.fromInt id , expect = Http.expectJson GotUser userDecoder userDecoder : Decoder User userDecoder = Decode.map3 User (Decode.field "id" Decode.int) (Decode.field "name" Decode.string) (Decode.field "email" Decode.string) main : Program () User Msg main = Browser.element init = \_ -> (getUser 1, getUser 1) , view = view , update = update , subscriptions = \_ -> Sub.none view : User -> Html Msg view user = div [] [ h1 [] [ text user.name ] , p [] [ text user.email ] ] update : Msg -> User -> (User, Cmd Msg) update msg user = case msg of GotUser (Ok newUser) ->

(newUser, Cmd.none) GotUser (Err _) ->

(user, Cmd.none) ``` This code uses the elm/http package to fetch a user from an API and display their name and email.

### Debugging and testing

Elm has some built-in features that make debugging and testing your code easier and more enjoyable. One of these features is the Elm debugger, which is a tool that lets you inspect and manipulate your app's state in the browser. You can enable the Elm debugger by using the Browser.application or Browser.document functions instead of Browser.sandbox or Browser.element. For example: ```elm main : Program () Model Msg main = Browser.application init = init , view = view , update = update , subscriptions = subscriptions , onUrlChange = UrlChanged , onUrlRequest = LinkClicked ``` When you run your app with the Elm debugger enabled, you will see a blue button at the bottom right corner of the screen. If you click on it, you will see a panel that shows your app's model and messages. You can also use some buttons to control your app's behavior, such as: - Pause: This pauses your app and lets you inspect its state. - Play: This resumes your app and lets it run normally. - Step: This steps through your app's messages one by one and shows how they affect the model. - Import: This lets you import a JSON file that contains a snapshot of your app's state. - Export: This lets you export a JSON file that contains a snapshot of your app's state. The Elm debugger is a great way to understand how your app works and find bugs. You can also use it to share your app's state with other developers or users for debugging purposes. Another feature that Elm provides is the elm-test package, which is a tool that lets you write and run automated tests for your code. You can install the elm-test package using npm: ```bash npm install -g elm-test ``` You can then create a tests folder in your project and write some test files inside it. A test file is a module that uses the Test and Expect modules from the elm-test package to define some test cases. For example, you can write a test file for the area function from the previous section: ```elm module AreaTest exposing (suite) import Expect import Shape exposing (Shape(..)) import Test exposing (..) suite : Test suite = describe "Area function" [ test "Circle with radius 5"

Expect.equal (area (Circle 5)) 78.53981633974483 , test "Rectangle with width 10 and height 20"

Expect.equal (area (Rectangle 10 20)) 200 ] ``` You can then run your tests using the elm-test command in your terminal: ```bash elm-test ``` This will compile and run your tests and show you the results. You can also use some flags to customize your testing experience, such as: - --watch: This runs your tests whenever you save a file. - --fuzz: This runs your tests with randomly generated inputs. - --seed: This sets the seed for the random inputs. - --report: This sets the format of the test report. The elm-test package is a great way to ensure that your code works as expected and prevent regressions. You can also use it to practice test-driven development (TDD), which is a technique that involves writing tests before writing code.

## Building a simple web app with Elm

Now that we have covered some of the basic concepts of Elm, let's build a simple web app with Elm. The app that we are going to build is a todo list app that lets you add, edit, delete, and mark tasks as done. To build this app, we are going to use the Elm architecture and some of the built-in modules that Elm provides. We are also going to use some external packages that we will install using elm install. Here are the steps to build the todo list app: - Define the model: The first step is to define the model for our app. The model is where we store our application state. In this case, our state consists of two things: a list of tasks and an input field for adding new tasks. Each task has an id, a description, and a status (done or not done). We can define our model as a record type with two fields: tasks and input. We can also define a type alias for our task type and a custom type for our task status. Here is how our model looks like: ```elm type alias Model = tasks : List Task , input : String type alias Task = id : Int , description : String , status : Status type Status = Done NotDone ``` - Define the initial model: The next step is to define the initial model for our app. The initial model is the state that our app starts with. In this case, our initial state is an empty list of tasks and an empty input field. We can define our initial model as a constant value that matches our model type. Here is how our initial model looks like: ```elm init : Model init = tasks = [] , input = "" ``` -