how to iterate inside the elements of a quosure of rlang in R

So let's say that I want to now if X appears in the quosure.

library(rlang)
library(purrr)
q <- quo(mean(X))

I know I can check for equality with expr

q[[2]][[2]] == expr(X)
[1] TRUE

But how do I iterate or flatten the quo element? flatten(q) doesn't work, I couldn't use for loops, no idea how to use some map function from purrr.

Ideally I would like to capture X when it's "data" and not any function.

Solution

I use the following custom function to convert expressions to their Abstract Syntax Trees (ASTs):

getAST <- function( ee ) { as.list(ee) %>% purrr::map_if(is.call, getAST) }

Since you're working with quosures, there's an intermediate step of retrieving the associated expression:

## Define a quosure
## Side note: don't use q as a variable name; it conflicts with q()
qsr <- quo( mean(5*X+2) )

## The associated expression
xpr <- rlang::get_expr( qsr )

## ...and its AST
ast <- getAST( xpr )
# List of 2
#  $ : symbol mean
#  $ :List of 3
#   ..$ : symbol +
#   ..$ :List of 3
#   .. ..$ : symbol *
#   .. ..$ : num 5
#   .. ..$ : symbol X
#   ..$ : num 2

From here, you can use standard techniques to find X. For example, flatten the nested list and compare each element to expr(X) as in your question:

purrr::has_element( unlist(ast), expr(X) )
# [1] TRUE

purrr::map_lgl( unlist(ast), identical, expr(X) )
# [1] FALSE FALSE FALSE FALSE  TRUE FALSE