Installation

npm install -g elm

Plugin elm.vim

Command line:

elm-repl like console
elm-reactor web server
elm-make Main.elm --output=main.html to compile
elm-package for downloading libs

Core language

values
- strings "asd" (concatenation "asdf" ++ "asdf")
- numbers 1 (integer division 5//2)

functions

-- function definitions
half n = n / 2
-- using unonymous function
half = \n -> n / 2
-- when it has two arguments than we can use partial application
divide x y = x / y
<function> : Float -> Float -> Float
-- it is the same as divide = \x -> (\y -> x / y)
divide 3
<function> : Float -> Float
divide 3 2
1.5 : Float

lists: all values must have same type
```
name = [ "Alice", "Bob" ]
```

tuples: can hold different types

import String
goodName name = \
  if String.length name <= 20 then \
    (True, "ok") \
  else
    (False, "nope")

records: key value pairs point = { x = 3, y = 4 }
- access with dot point.x
- access functions is when variable starts with dot .name person1
```
List.map .name [ {name='Dule'}, ]
```
- pattern matching (extrapolation) inside function arguments with {arg}
```
under70 {age} = age < 70
```
- update values with pipe (non destructive, it will create new attribute and share existing attributes) { point | x = 1 }
- difference with js objects is that you can’t ask for nonexisting field, all fields are defined

types

type annotations are written statement for types of arguments and output
```
name : String
name = "Dusan"

add : Int -> Int
```

type alias is used short type annotations

type alias User =
  { name: String
  , bio: String
  }

union types is used to create new type with new values

type Visibility = All | Active | Completed
-- All is type of Visibility ie All : Visibility
f : Visibility -> String
f visibility =
  case visibility of
    All ->
      "all"
-- all case posibilities are checked by compiler

type Msg
  = Change String
-- in this declaration new constructors are created Change: String -> Msg

type IntList = Empty | Node Int IntList
-- linked list is recursive: Node 64(Node 42 Empty)

type List a = Empty | Node a (List a)
-- generic linked list

use backslash \ to split in multiple lines

User input

import Html exposing (

-- MODEL
type alias Model = {

-- UPDATE
type Msg = Reset |
update : Msg -> Model -> Model
update msg model =
  case msg of
    Reset -> ...

-- VIEW

view : Model -> Html Msg
view model =

Examples

pairs.one game in elixir and phoenix

tutorial todo https://guide.elm-lang.org/get_started.html

http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html https://www.toptal.com/front-end/make-web-front-end-reliable-with-elm https://www.youtube.com/watch?v=28jCDXfZCgE#t=0.417205

monads for rubyist

Haskell Books

how to think in haskell Maybe Haskell
understanding syntax Learn You a Haskell

Monads

https://stackoverflow.com/questions/3870088/a-monad-is-just-a-monoid-in-the-category-of-endofunctors-whats-the-problem

Elm functional static typed language

Contents