Calling lookup::lookup changes behaviour for rest of session

So that when I print a function, the source appears in RStudio

I guess this is because we register an S3 method for functions, which is then loaded when the namespace is loaded

#' @export print.function

This should be switched to only happen when lookup is attached, which I guess implies the S3 registration has to be done with registerS3method() in .onAttach().

Yeah, I think that makes sense.

This sort of hints that maybe lookup can't be a CRAN package, because it's rude to declare a method if you own neither method nor generic? Maybe it would be better to require the use to specifically opt-in? i.e. by calling lookup::auto() which would register the method dynamically.