Elm Lang Guide

2019-07-19_elm-language-guide.md

Elm Language Guide

• 📆 2019-07-19
• this spans many weeks / investment times
• 📖 🌳️🕵‍♀️️ The Elm Language Guide
• 👨‍💻📝️ an experienced OOP programmer learning FP and Elm

Installing Elm

Compared to my experiences using JavaScript over many years, I found installing
and running Elm to be fast and easy for an Ubuntu 18 development machine.

Running this step was required, and deduced from a few different github issue
comments:

sudo npm install -g elm --unsafe-perm=true --allow-root

Core Language

The elm REPL is really nice to use.

Records

• Records vs Objects is interesting
  • you cant ask a Record for a field that does not exist
  • a Record never has an undefined or null field
  • a Record can not be made recursive with this or self keyword
    • 📝️ Elm tries to avoid systemic problems from OOP by forcing separation of
      data and logic. The ability to say this breaks this separation.
  • a Record supports structural typing
    • dont care about the names or location in call stack something was defined
    • only care that, for every a and b, the b has at least every single
      feature that a has.
      • this differs from duck typing, where one might only care that b has
        at least the current interesting features that a has.

The Elm Architecture

if you ultimately cannot use Elm at work yet, you will get a lot out of using
Elm and internalizing this pattern.

...after joining a company that provides developers with ample skill investment
time and resources 😊

Intro

The Basic Pattern

• Model - describes the application state
• Update - describes the ways state can be updated
• View - represents the application state as HTML

Follow Along

There is a repository to facilitate coding along with this guide. I have made
my own fork here: 🍴

Buttons

• see buttons code

• skimming types

  • cool Elm has type inference
  • it helps catch bugs! 🐛️
  • actually not sure why the guide says to skim this part right now, I just want to read all the things ¯\_(ツ)_/¯

• types can be used to describe capabilities as data

  • e.g., a type of Increment or Decrement is a piece of data that is also describing a capability

• so, I understand how this produces an HTML view that sends messages, but how does this program actually receive the messages? the connection is not obvious to me at a glance at this extremely simple code 🤔️

• Model, Update, View - the essense of The Elm Architecture ™️

  • 🌳️🌳️🌳️

• I took on the programming challenge at the end, to make a Reset button. I spent a lot of time figuring out how to reassign model to 0! Like several other folks on stackoverflow, I diddnt see the = at the top of the function definition!

  • PR #1

Text Fields

• Im starting to wonder what Msg -> Model -> Model means for the func def 🤔️

  • does this mean: receives a Msg and a Model and returns a Model ?
  • whats the -> mean in this context?

• ok, the program here mainly just persists the value you type

  • the actual reversal of String is done by JS on the front end, all the Elm app does is accept a string and return it to the front end.
  • other than to highlight the change to use a Record to represent Model, I am not sure if this is a worthwhile example on its own 🤷‍♀️️

Forms

• 🤔️ what is exposing(..)❓

  • imports all of the things 🙌

• Forms seem pretty straightforward to me.

  • I do find that an absence of learning Elm makes remembering its styntax difficult!

• TODO mess with the code as the example suggests!

• cya next time!

🚧🏗👷