Abstract-task-do.md

@ do syntax

This is a generalization of the async/await syntax, switching out async for @___ and await for do. I don't think we should consider this for 0.15, but it shows where we might want to take things longer term. In this world, a task example looks like this:

  @task
    [ do print 3
    , do print 4
    , do print 5
    ]

A maybe example looks like this:

add : Maybe Int -> Maybe Int -> Maybe Int
add mx my =
  @maybe
    do mx + do my

Making the main module a task

It is kind of interesting because we can give it a meaning when we add @task to a module declaration:

@task module Main where

mb = do mailbox

...

Haxl

This is cool because Haxl type stuff fits in really easily.

  @haxl
    [ do get user "http://example.com/alice"
    , do get user "http://example.com/bob"
    , do get user "http://example.com/candice"
    ]

And things would all go in parallel.

Http.elm

getImage : (Int,Int) -> String -> Task Http.Error String
getImage dimensions tag =
  @task
    let
      searchUrl =
        flickrUrl "search" [ ("sort", "random"), ("per_page", "10"), ("tags", tag) ]

      photos =
        do Http.get photoList searchUrl

      photo =
        do Task.fromMaybe photoErr (List.head photos)

      sizes =
        do Http.get sizeList (flickrUrl "getSizes" [ ("photo_id", photo.id) ])

      pickSize =
        sizes
          |> List.sortBy (sizeRating dimensions)
          |> List.head
          |> Task.fromMaybe sizeErr
    in
      do pickSize

Json.elm

field : String -> JS.Decoder a -> JS.Decoder a
index : Int -> JS.Decoder a -> JS.Decoder a

person : Decoder Person
person =
  @decoder
    let position =
          @decoder (do index 0 JS.float, do index 1 JS.float)
    in
        Person
          (do ("name" => JS.string))
          (do ("age" => JS.int))
          (do ("position" => position))

Maybe.elm

add : Maybe Int -> Maybe Int -> Maybe Int
add maybeLeft maybeRight =
  @maybe
    do maybeLeft + do maybeRight

Random.elm

person : Generator Person
person =
  @generator
    Person
      (do Gen.string)
      (do Gen.int)
      (Location (do Gen.int) (do Gen.int))


type alias Person =
  { fullname : String
  , age : Int
  , location : Location
  }


type alias Location =
  { longitude : Int
  , latitude  : Int
  }