-> (a -> a) -> Operator String u Identity a
prefix  name fun       = Prefix (do{ reservedOp name; return fun })
postfix name fun       = 
prefix, postfix :: String -> (a -> a) -> Operator String u Identity a
prefix  name fun       = Prefix (do{ reservedOp name; return fun })
prefix  name fun       = Prefix (do{ reservedOp name; return fun })