extractPDo (DoBindP _ p1 p2 ps)  = let (ps1, ps2) = unzip ps
                                       ps'        = ps1 ++ ps2
                                   in  concatMap extract (p1 : p2 : ps')
extractPDo (DoBindP _ p1 p2 ps)  = let (ps1, ps2) = unzip ps
                                       ps'        = ps1 ++ ps2
                                   in  concatMap extract (p1 : p2 : ps')
extractPDo (DoBindP _ p1 p2 ps)  = let (ps1, ps2) = unzip ps
                                       ps'        = ps1 ++ ps2
                                   in  concatMap extract (p1 : p2 : ps')