Handle row polymorphism for records

[emilyhorsman]

e.g.,

import Html exposing (..)


type alias State a =
    { a | count: Int }

type alias MoreState =
    State { test: Int }

increment : State a -> State a
increment s = { s | count = s.count + 1 }

state : MoreState
state =
    { count = 0
    , test = 1
    }
    |> increment
    |> increment

main = text (String.fromInt state.count)