What this repo contains

This repo contains

A text file (TryStuffInTheRepl.elm) with Elm language snippets that can be run in the Elm REPL
Several little stand-alone Elm apps demonstrating various features (all created with the create-elm-app program)
A very short PowerPoint presentation in the PowerPoint folder

Creating an elm App

npm install create-elm-app -g
create-elm-app my-app
cd my-app/
elm-app start

Links to Elm Information

VSCode Extension for Elm language Support

The repo for this extension is at https://github.com/elm-tooling/vscode-elm. However, you install the extension directly in VSCode (search the Extensions Marketplace)

Language Snippets

The root folder contains the file TryStuffInTheRepl.elm

If you install the VSCode Extension for Elm language Support, you can

send single line commands to the REPL with the VSCode command:

ELM: REPL - Send Line
multi-line commands to the REPL with the VSCode command:

ELM: REPL - Send Selection

You can go through this file and execute the lines in order to get a feel for the Elm language. Don't send the comment lines as they aren't recognized by the REPL

Sample Apps

Each of the Elm Apps in this repo are stand-alone and were initially created with the create-elm-app program. To run the sample, cd into the folder and invoke:

elm-app start

Basic Rendering

This is the most basic app and is unmodified from what is created by the create-elm-app program. But it is useful to look at to see how an Elm program is bootstrapped and how the view is rendered.

cd BasicRendering
elm-app start

SimpleCommandDemo

This app demonstrates how commands can be generated by the Elm runtime in response to user-input events (in this case via a button's onclick function.). It also demonstrates how these commands wrap your Msg type and how they route back into the program via the update function so that you can, in response, update the model appropriately (in this case incrementing and decrementing an integer.)

cd SimpleCommandDemo
elm-app start

GettingARandomNumber

Functions in Elm are pure. They must (and will) always return the same output for the same input and produce no side effects. Operations that would cause a violation of this principle are handled by the Elm runtime so that your code is purely functional.

Examples of operations that must be handled by the runtime include:

Handling user input
Getting the date or time
Generating a random number
Calling a Web API
Calling into raw JavaScript (via Interop)

This example demonstrates getting input through text boxes and building a command (Cmd) to have the runtime generate a random number which is then returned as a custom Msg type to your update function.

cd GettingARandomNumber
elm-app start

SubscriptionDemo

The previous examples demonstrate how Cmds are used to cause the Elm runtime to execute an impure operation and return the results to your update function via a custom Msg type. Hand-in-hand with Cmds are Subscriptions. Subscriptions allow you to have the Elm runtime stream events into your application safely wrapped in a custom Msg.

This example demonstrates two separate subscriptions:

The current time. This subscription causes the time to be sent to your update function in the form of a custom Msg once a second.
Mouse movements. This subscription causes the position of the mouse to be sent to your update function in the form of a custom Msg whenever the mouse's position changes.

The example also shows how to handle more then one subscription.

cd SubscriptionDemo
elm-app start

Websockets

This example demonstrates how the Elm subscription mechanism is used to interact with a server over Web Sockets. The example requires a server (startup instructions below)

First start a simple node websocket server application

cd Websockets/Server
node main.js

Then run the Elm app

cd Websockets
elm-app start

hpinsley/ElmPresentation