call(
  a,
  b,
  c
)

call(
  a, b,
  c
)

call(a, )
call(a, )

call(a, )

mpg %>%
  summarise(
    avg_cty = mean(cty),
    avg_hwy = mean(hwy),
    n = n(),
    n_class = n_distinct(class)
  )