.x 和 .y 仅在有两个参数时指定.如果超过 2 个，我们可以按出现顺序使用 ..1, ..2, ..3

The .x and .y are only specified when there are two arguments. With more than 2, we can use ..1, ..2, ..3 in their order of occurrence

library(purrr)
accumulate2(1:5, 1:4, ~2*..1 + 3*..2 +..3)
#[[1]]
#[1] 1

#[[2]]
#[1] 9

#[[3]]
#[1] 29

#[[4]]
#[1] 73

#[[5]]
#[1] 165