get browsing state in a function

Question

I have a function such as this one :

fun <- function() {
  browser()
  is_browsing()
} 

I would like to know what the code of is_browsin

Answer 1

When you use the browser, the prompt shows you the browse level :
Browse[1], Browse[2],...

> browser()
Called from: top level 
Browse[1]> browser()
Called from: top level 
Browse[2]> 

This browse level is calculated in main.C by :

browselevel = countContexts(CTXT_BROWSER, 1);

Where CTXT_BROWSER is a constant defined in defn.h:

CTXT_BROWSER  = 16

You could use this internal countContexts function to get the is_browsing information you're looking for :

is_browsing.cpp

#include 
#include 
#include 
using namespace Rcpp;


// [[Rcpp::export]]
int is_browsing() {
  return Rf_countContexts(16,1);
}

Test :

library(Rcpp)
sourceCpp('is_browsing.cpp')
test <- function() {
  is_browsing()
}

test()
#> [1] 0

browser()
#> Called from: eval(expr, envir, enclos)

test()
#> [1] 1

^{Created on 2020-08-29 by the reprex package (v0.3.0)}

Also working if browser is called within function :

test2 <- function() {
  browser()
   is_browsing()
 }
test2()
Called from: test2()
Browse[1]> n
debug à #3 :is_browsing()
Browse[2]> n
[1] 1

If you wanted a TRUE / FALSE return, the Rcpp code would be:

#include 
#include 
#include 

// [[Rcpp::export]]
Rcpp::LogicalVector is_browsing() { 
  return Rf_countContexts(16,1) > 0;
}