adjustErrP :: XParser a -> (String->String) -> XParser a
p `adjustErrP` f = p `onFail` do pn <- posn
                                 (p `adjustErr` f) `adjustErr` (++show pn)
adjustErrP :: XParser a -> (String->String) -> XParser a
p `adjustErrP` f = p `onFail` do pn <- posn
                                 (p `adjustErr` f) `adjustErr` (++show pn)
p `adjustErrP` f = p `onFail` do pn <- posn
                                 (p `adjustErr` f) `adjustErr` (++show pn)