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

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

Haskell Books