Runtime error in Elm due to shadowing

readme.markdown

This code produces a runtime error due to shadowing in Elm (Platform version 0.15.1).

The error is Cannot use 'in' operator to search for '_' in undefined. The error happens somewhere in the code for the equals/not-equals comparison in the function given to filter, because one of the objects which are compared for equality (current) is undefined at that time due to the shadowing.

elm/compiler#1018 is probably related. IMHO, this case should even be compile error, not only a warning.

Main.elm

import Html

type alias Model = { a : String }

one = { a = "1" }
two = { a = "2" }

getNext : Model -> Model
getNext current =
  let
    -- the identifier "current" is shadowed here
    (current :: rest) = List.filter (\ p -> p /= current) [ one, two ]
  in
    List.head rest |> Maybe.withDefault one

main : Html.Html
main =
  let model = getNext one
  in Html.text model.a