DoNotation.elm

with Task.andThen do
  issues = Http.get "/issues.json"
  milestones = Http.get "milestones.json"
in
  assignMilestones (issues, milestones)
  
-- This would desugar to:

Task.andThen
  (Http.get "/issues.json")
  (\issues ->
    Task.andThen
      (Http.get "milestones.json")
      (\milestones ->
        assignMilestones (issues, milestones)))

WithMaybe.elm

type Person = Person { name : String, age : Int }

with Maybe.andThen do
  name = Dict.get names id
  age = Dict.get ages id
in
  Person { name = name, age = age }
  
-- desugar

Maybe.andThen
  (Dict.get names id)
  (\name ->
    Maybe.andThen
      (Dict.get ages id)
      (\age ->
        Person { name = name, age = age }))
        
-- even better

body : (Maybe a -> Maybe b) -> Person
body = do
  name = Dict.get names id
  age = Dict.get ages id
in
  Person { name = name, age = age }
  
with : (m a -> m b) -> ((m a -> m b) -> c) -> c
with f body = body f

withMaybe : ((Maybe a -> Maybe b) -> c) -> c
withMaybe = with Maybe.andThen
  
result = withMaybe body