p_seq open close elem = 
  between (open >> spaces) (spaces >> close) $
    elem `sepBy` (spaces >> char ',' >> spaces)
p_seq open close elem = 
  between (open >> spaces) (spaces >> close) $
    elem `sepBy` (spaces >> char ',' >> spaces)
p_seq open close elem = 
  between (open >> spaces) (spaces >> close) $
    elem `sepBy` (spaces >> char ',' >> spaces)