[Roxygen-devel] parameters with default NULL value

[Melissa Jane Hubisz]

Hello,
I've been developing a fairly large package in R and was thrilled to
discover roxygen.  Thank you for providing this useful tool!

I  have been using the most recent version of roxygen from the SVN
repository.  One problem I have encountered is that the "usage" is not
displayed properly if a function has parameters whose default value is
NULL.  For example, the function:
myfunc <- function(a, b=NULL, c=0) {NULL}

will have the documentation:
Usage:
  myfunc(a, b, c=0)

which incorrectly implies that b is a required parameter.

I did a bit of poking around and this seems to have a simple fix, by
changing the function parse.formals in parse.R to:

parse.formals <- function(expressions) {
  formals <- NULL
  call <- car(expressions)
  if (is.call(call)) {
    f <- cadr(expressions)
    if (is.function.definition(f))
      formals <- tryCatch(formals(eval(call)),
                          error=function(e) NULL)
  }
  if (is.null(formals)) formals
  else list(formals=Map(function(formal)
              if (is.null(formal)) 'NULL'                #THIS IS THE
ONLY CHANGE, it used to be the empty string ''
              else if (is.call(formal)) capture.output(formal)
              else as.character(maybe.quote(formal)), formals))
}

Not being very familiar with the inner workings of roxygen, I'm not
sure if this hack will break anything else, but it seems to work for
me.  If it is a proper solution, could it be incorporated into
roxygen?  If not, is there another way to fix this?

Thanks again for your work on this.  It's been a huge timesaver for me.
-Melissa

Melissa Hubisz
Department of Biological Statistics and Computational Biology
Cornell University