how to determine if a function's result is invisible

Suppose we have a function such as the following

F <- function(f, x) f(x)+1

which runs function f and then transforms it.  I would like the
corresponding function which works the same except that
unlike F returns an invisible result if and only if f does.

Is there some way of determining whether f returns
an invisible result or not?

Thus we want this:

f <- function(x) x
g <- function(x) invisible(x)

F(f, 1)

2

F(g, 1)

I don't think there's a way to do that.  Internally there's a global 
flag called R_Visible; if it is set to zero, the value won't print.  But 
  it gets reset to 1 very easily (e.g. by adding 1 to the result of an 
invisible function), and it's not available in the API for you to write 
C code to look at it.

I think you'll just have to do require the user of your F to tell you 
that they want the result to be invisible.

Duncan Murdoch