Question

This is crazy, and just out of intellectual curiosity: Can I run a function in R in such a way that after the function completes I can get all variables created when the function executed? So the ability to look into a function right before it returned? I don’t mean entering the function in debug mode.

Answer 1

I’m not sure if this is what you want, but maybe close.
You can embed an arbitral expression in existing functions by trace:

> trace(lm, exit = function().last_env <<- parent.frame())
Tracing function "lm" in package "stats"
[1] "lm"
> lm(y~x, data.frame(x=1:10, y=10:1))
Tracing lm(y ~ x, data.frame(x = 1:10, y = 10:1)) on exit 

Call:
lm(formula = y ~ x, data = data.frame(x = 1:10, y = 10:1))

Coefficients:
(Intercept)            x  
         11           -1  

> ls(.last_env)
 [1] "cl"          "contrasts"   "data"        "formula"     "m"           "method"      "mf"          "model"       "mt"          "na.action"   "offset"     
[12] "qr"          "ret.x"       "ret.y"       "singular.ok" "subset"      "w"           "weights"     "x"           "y"           "z"          
> get("cl", .last_env)
lm(formula = y ~ x, data = data.frame(x = 1:10, y = 10:1))