parsing onClick location in Elm

gistfile1.elm

import Json.Decode as Decode

decodeClickLocation : Decode.Decoder (Int,Int)
decodeClickLocation =
    Decode.object2 (,)
        (Decode.object2 (-)
            (Decode.at ["pageX"] Decode.int)
            (Decode.at ["target", "offsetLeft"] Decode.int)
        )
        (Decode.object2 (-)
            (Decode.at ["pageY"] Decode.int)
            (Decode.at ["target", "offsetTop"] Decode.int)
        )