
WISHLIST

o assign("mywarn", NULL, .GlobalEnv)
  fn$tryCatch( warning("a warning"), 
    warning = w ~ mywarn <<- conditionMessage(w))
  print(mywarn)
does not work.

o xml features

o better simplification

o handle invisible output

o extend fn$ to proto objects

o can current rules of determining which formulas to convert to functions
  and which strings to perform interpolation on be improved?

