Highway

to

Elm

Highway

to

Elm

http://besnier.se/elm-workshop/

Front-end is dominated by

JavaScript is backward compatible

Biggest advantage

Biggest disadvantage

You can't deprecate things !!! 😱

null > 0  // false

null == 0 // false

null >= 0 // ... true

JS syntax size

Time

ES6

A LOT to learn!

The language is complex
Many ways to do the same thing
Framework choice / learning
Tooling

Hard to optimize

Dead code elimination / Tree shaking
Assets size
Complex build

Low confidence level

Minor IDE assistance
Refactoring is painful
Slow feedback cycle: runtime
Dependencies are risky

How one developer just broke Node, Babel and thousands of projects in 11 lines of JavaScript

By Chris Williams

Details about the event-stream incident

Elm is a typed functional language to create fast and reliable web applications

Websites and webapps

Domain specific

Statically typed

Many bugs don't compile
IDE can help you
Refactoring is compiler-driven
Feedback cycle is really fast

No Runtime Exceptions

17K+ LoC

200K+ LoC

Declarative, not imperative

const myNumbers = [1, 2, 3, 4, 5];
let squaredNumbers = [];

for(number of myNumbers) {
    squaredNumbers.push(number * number);
}

const myNumbers = [1, 2, 3, 4, 5];
const squaredNumbers = myNumbers
    .map(number => number * number);

Honesty

function sendEmail(user) {
    



}

No unwanted side-effect

function sendEmail(user) {
    if (user.email === null) {
        throw new Error('No email provided for the user');
    }    

}

function sendEmail(user) {
    if (user.email === null) {
        throw new Error('No email provided for the user');
    }    
    launchNuclearMissile();
}

Side-effect = command, explicitely declared

Fast

Everything is pure => optimizations
Small assets

"Elm has a very strong emphasis on simplicity, ease-of-use, and quality tooling."

Simplicity, ease of use

Focused on one purpose
Syntax removal
Well-thought API
Compiler helps you
Explicitness

Quality tooling

Compiler
Project starter
Package manager
Dev environment
REPL
Tests runner
Doc tool

Enforced documentation

package.elm-lang.org/packages/jgrenat/elm-html-test-runner/1.0.1

Enforced versioning

1.2.3

Nothing changed for the outside

Something was added

Something has changed

Great community

See also Building Trust: What Has Worked by Richard Feldman

and What is success? by Evan Czaplicki

Syntax

-- a single line comment

{- a 
   multiline 
   comment
-}

Comments

Advantages

Great developer experience
No runtime exceptions
Great debugger
Powerful type system
Great performances
Great community

Drawbacks

Opinionated governance model
Boilerplate vs Explicitness
Not for every use case

Why use Elm?

Complex UI / Model
Frequent refactoring
You care for bugs
Easy introduction to FP
Write better code

http://besnier.se/elm-workshop/