Why does purrr::map not support quasiquotation?

Question

I'm curious why the purrr::map_* function family, despite being a part of tidyverse, does not support quasiquotation by splice-unquoting its dots prior to evaluation of the mapped function?

library(tidyverse)
library(rlang)

set.seed(1)
dots <- quos(digits = 2L)

# this obviously won't work
purrr::map_chr(rnorm(5L), 
               ~ format(.x, !!!dots))
#> Error in !dots: invalid argument type

# I'm confused why this does not work
purrr::map_chr(rnorm(5L), 
               ~ format(.x, ...), 
               !!!dots)
#> Error in !dots: invalid argument type

# Finally, this works
eval_tidy(expr(
  purrr::map_chr(rnorm(5L), 
                 ~ format(.x, ...), 
                 !!!dots)
))
#> [1] "1.5"   "0.39"  "-0.62" "-2.2"  "1.1"

Created on 2019-01-31 by the reprex package (v0.2.0).

DiceboyT DiceboyT · Accepted Answer · 2019-01-31T23:24:05

I think the problem is format does not support tidy dots -- you can use exec to force a function to be able to use them:

library(tidyverse)
library(rlang)

set.seed(1)

nums <- rnorm(5L) #for some reason couldn't replicate your numbers
nums
#[1] -0.6264538  0.1836433 -0.8356286  1.5952808  0.3295078

dots <- exprs(digits = 2L)

map_chr(nums, ~exec(format, .x, !!!dots))
#[1] "-0.63" "0.18"  "-0.84" "1.6"   "0.33"

You also need to use exprs not quos to capture the additional function arguments for this to work (not entirely sure why quos doesn't work here though, to be honest).

Why does purrr::map not support quasiquotation?

1 Answers