This works, and the
paste()pattern is so useful we suggest researching and memorizing it.
However the “call” portion of the model is reported as “
formula = f” (the name of the variable carrying the formula) instead of something more detailed. Frankly this printing issue never bothered us. None of our tools or workflows currently use the model
callitem, and for a very large number of variables formatting the call contents in the model report becomes unweildy. We also already have the formula in a variable, so if we need it we can save it or pass it along.
There is a much better place on many models to get model structure information from than the model
callitem: the model
termsitem. This item carries a lot of information and formats up quite nicely:format(terms(model)) #  "mpg ~ cyl + disp + hp + carb"
Be sure to check out the comments too, as there are several solutions to this problem.