Variables can't be negated with a minus

[tunguski]

Taken extracted from https://raw.githubusercontent.com/rundis/elm-bootstrap/3.0.0/src/Bootstrap/Popover.elm

calculatePos pos { rect, offsetWidth, offsetHeight } =
            { left = -offsetWidth
            , top = (rect.height / 2) - (offsetHeight / 2)
            }

[tunguski]

left = -offsetWidth is problematic here

[wende]

Seems that generally - doesn't work before any variable name