Apply/map R function formals into new function body from code as string

Question

I want to take a user\'s code and convert reactive() calls into functions like this.

a <- reactive({
  i         


        

Answer 1

This is inspired by data.table's way of replacing its .() alias.

code <- 
    "library(shiny)

  input <- list(cty = 15)
  
  df <- reactive({
    x <- input$cty
    mpg %>% filter(cty < x)
  })
  
  n_obs <- reactive(head(df()))"

all_expr <- parse(text = code)

f_recurse_look = function(e) {
    if (is.call(e)) {
        if (e[[1L]] == "reactive")
            e = as.function(as.list(e)[-1L])
        else
            for (i in seq_along(e)[-1L]) if (!is.null(e[[i]])) e[[i]] = f_recurse_look(e[[i]])    
    }
    e
}

lapply(all_expr, f_recurse_look)
#> [[1]]
#> library(shiny)
#> 
#> [[2]]
#> input <- list(cty = 15)
#> 
#> [[3]]
#> df <- function () 
#> {
#>     x <- input$cty
#>     mpg %>% filter(cty < x)
#> }
#> 
#> [[4]]
#> n_obs <- function () 
#> head(df())

This approach will recursively look through the expression calls until it finds reactive. Note, this means that if reactive is in multiple calls in a single expression, this solution would need modified.