Sample function doesn't work well with purrr::rerun and pipe?

Question

I observed some weird behavior in purrr::rerun when it's used with %>% that I couldn't understand.

If I run,

library(purrr)
sample(1:30, 3) %>% rerun(4, .)

it will return,

# 1 24 5
# 1 24 5
# 1 24 5
# 1 24 5

clearly it's not what I want.

However, if I run a similar code without %>%, it will actually work as expected.

rerun(4, sample(1:30, 3))

# 17 5 20
# 13 3 6
# 22 25 3
# 20 30 29

I couldn't understand why the behavior is different. Can someone explain? Thanks in advance.

Answer 1

magrittr doesn't evaluate the dots lazily. It might very well have, as in this mock pipe (don't use it it will break easily!)

`%foo>%` <- function(e1,e2){
  eval.parent(eval(substitute(substitute(e2,list(. = substitute(e1))))))
}

sample(1:30, 3) %foo>% purrr::rerun(4, .)
#> [[1]]
#> [1] 22 25  9
#> 
#> [[2]]
#> [1] 14 28 21
#> 
#> [[3]]
#> [1]  4  1 25
#> 
#> [[4]]
#> [1] 17  2 25

^{Created on 2019-09-19 by the reprex package (v0.3.0)}

It is a design choice, probably made to avoid ambiguities and inefficiency when several dots are used.