The Elm Talk

Abhishek Yadav

ப்ரோக்ராமர்

Co-organizer: Chennai.js

@h6165

The agenda

Elm

• The goal and the claims
• Functional programming
• Type system
• The Ecosystem
• Challenges

The goal and the claims

Elm

• No run-time errors
• Reactive UI

Introduction

Elm

Elm is a typed, pure functional programming language that compiles to Javascript.

typed: values and functions have types. Various type concepts are supported - type checking, inferred types, generics, union types, algebraic data types. There are no typeclasses

functional: functional programming concepts are supported (anonymous functions, higher order functions, currying, immutability etc)

Compiles to Javascript: Implements a Virtual-dom, supports Redux-like pattern, and (kind of) components. Provides module system and build tooling.

Introduction

Elm

Practically speaking ...

Typed: catch errors by compiling

Functional: no internal state. no mutables.

Compiles to Javascript: Run in browser, React+Redux+Webpack

No run time errors

Elm

What errors ?

The most common ones -

• Undefined is not a function
• NaN

We forgot to check for undefined/null values

We did math on a non-number

No run time errors

Elm

Type checking can help with both

-- total is a function that takes two Int values,
-- and produces an Int value


total: Int -> Int -> Int
total x y =
  x + y


-- This will fail compilation

total 2 "2"

No run time errors

Elm

And for empty values, it forces us to handle them

-- total is a function that takes two Int values,
-- and produces an Int value


showFirst: List a -> String
showFirst myList =
  case (List.head myList) of
    Just x ->
      toString x
    Nothing ->
      ""
   

-- 1. List.head gives a value of Maybe type
-- 2. Will fail compilation if we don't handle the Nothing case