elm,
a delightful language
for learning
functional programming
@kajetansw
kajetan.dev
Kajetan Świątek
👨🎨 Front-end developer
🇵🇱 Wrocław
Why should you be interested in FP?
What is Elm?
Why should you at least try it?
Other FP languages that compile to JS
Elm vs TypeScript
Why should you be interested in FP?
1
pure functions
2
IMMUTABILITY
3
easier testing
4
constant growth
5
BROADENS YOUR MIND
What is Elm?
What is Elm?
why should you try it?
ADVANTAGES OF THE FP WORLD
1
Immutability
2
PURE FUNCTIONS
3
EASIER TO TEST
4
BROADENS YOUR MIND
5
CONSTANT GROWTH
SMALL(ISH) LEARNING CURVE FOR JS DEVELOPERS
Easier*
* subjective; relatively, in comparison
Harder*
THE ELM architecture
Model
View
Update
render
message
Elm runtime
command
message
THE ELM ARCHITECTURE
type alias Model = Int
init : Model
init = 0view : Model -> Html Msg
view model =
div []
[ button [ onClick Decrement ] [ text "-" ]
, text (String.fromInt model)
, button [ onClick Increment ] [ text "+" ]
]
type Msg
= Increment
| Decrement
update : Msg -> Model -> Model
update msg model =
case msg of
Increment ->
model + 1
Decrement ->
model - 1Model
View
Update
render
message
no runtime errors.
getHero : String -> Cmd Msg
getHero url =
Http.get
{ url = url
, expect = Http.expectJson HeroReceived heroDecoder
}Fetching data via HTTP requires data decoder
no 'null' or 'undefined'.
type Maybe a
= Just a
| Nothing
sanitize : String -> Maybe Int
sanitize input =
String.toInt (String.trim input)
getDefault : Maybe Int -> Int
getDefault input =
case input of
Just i -> i
Nothing -> 0Sanitizing user's input
GREAT COMPILER ERROR MESSAGES
elm vs typescript
elm vs typescript
*
*
**
*
* disadvantage comes from the nature of JavaScript
Prevents runtime data inconsistency
(API changes, etc.)
No `null` and `undefined`
Immutability
No `any` or `unknown` type
Prevents poor typing from 3rd-party libraries
Easy to adopt in existing project
** mutability can be good when used properly (e.g. when comes to the performance)
elm vs typescript
fp libraries for ts
fp-ts
@effect-ts/core
other fp languages that compile to js
other fp languages that compile to js
examples of elm apps
elm-survey-app
elm learning resources
- Beginning Elm
- Official docs
- Awesome Elm on GitHub
- "Let's be mainstream! User focused design in Elm" talk by Evan Czaplicki
Thank you!
✋😎
@kajetansw
kajetan.dev
Elm, a delightful language for learning FP
By Kajetan Świątek
