op_base(x, vars, class = character())op_single(name, x, dots = list(), args = list())
add_op_single(name, .data, dots = list(), args = list())
op_double(name, x, y, args = list())
op_grps(op)
op_vars(op)
op_sort(op)
op_vars()
and op_grps()
compute the variables and groups from
a sequence of lazy operations. op_sort()
tracks the order of the
data for use in window functions.