[Haskell-cafe] Problem about pattern matching.

Hi, I have code as below. How come "case" version works wrong and gives me "overlap" compiling warning? Thanks. if dayOfMonth == firstDayOfMonth then v day (x, y) else if dayOfMonth == lastDayOfMonth then not_ $ v day (x, y) else Mider day (x, y) case dayOfMonth of firstDayOfMonth -> v day (x, y) lastDay -> not_ $ v day (x, y) _ -> Mider day (x, y) -- 竹密岂妨流水过 山高哪阻野云飞