Question

If I have a few interconnected functions, then it can be useful to trace the path through them. That is using the trace function to give a message each time R enters or leaves one of the functions. For example,

f <- function() g()
g <- function() h()
h <- function()
{
 if(runif(1) > 0.3) g() else 99
}

trace_my_fns <- function()
{
  fn_names <- c("f", "g", "h")
  invisible(trace(
    fn_names,
    tracer = quote(0),
    exit   = quote(0),
    where  = globalenv()
  ))
}

trace_my_fns()
set.seed(4)
f()

When I’m finished with this tracing, I need to untrace them.

untrace_my_fns <- function()
{
  fn_names <- c("f", "g", "h")
  invisible(trace(
    fn_names,
    where = globalenv()
  ))
}
untrace_my_fns()

For some reason, this isn’t untracing the functions properly. To see this, take a look at

f
body(f)

If I directly call untrace on each function, for example untrace(f) at the commmand line, it works. How should I create a function to untrace all my functions at once?

Answer 1

Well, change to:

untrace_my_fns <- function()
{
  fn_names <- c("f", "g", "h")
  invisible(untrace(
    fn_names,
    where = globalenv()
  ))
}

untrace_my_fns()
set.seed(4)
f() # no more tracing...

…because you called trace instead of untrace!