Code compiles, but the circular dependency of the two signals causes foldp to receive an 'undefined' input signal in the JS. Should be a compilation error.

ElmCompilerBug.elm

import Graphics.Element exposing (show, Element)
import Mouse


-- VIEW

main : Signal Element
main = 
  Signal.map view model


view : Model -> Element
view model =
  show model


-- UPDATE

update : Input -> Model -> Model
update {prev, position} model =
  if prev == model
    then position :: model
    else model


-- MODEL

type alias Model = List Int

model : Signal Model
model = 
  Signal.foldp update [] input


-- SIGNALS

type alias Input =
  { prev : Model
  , position : (Int, Int)
  }


input : Signal Input
input =
  Signal.sampleOn Mouse.clicks <|
    Signal.map2 Input
      model
      Mouse.position