[Rd] page() (Was: Re: predict.smooth.spline.fit and Recall() (Was: Re: Return function from function and Recall()))

[Prof Brian Ripley]

On Wed, 5 Apr 2006, Henrik Bengtsson wrote:

> Here I think S3 dispatch is very natural.  Try the following:

I don't: it is documented to work on a name not an object.

> page <- function(x, method = c("dput", "print"), ...) UseMethod("page")
>
> page.getAnywhere <- function(x, ..., idx=NULL) {
>  name <- x$name;
>  objects <- x$obj;
>
>  if (length(objects) == 0)
>    stop("no object named '", name, "' was found");
>
>  if (is.null(idx)) {
>    # Include all non-duplicated objects found
>    idx <- (1:length(objects))[!x$dups];
>  }
>
>  for (ii in idx) {
>    title <- paste(name, " (", x$where[ii], ")", sep="");
>    eval(substitute({
>      object <- x$obj[[ii]];
>      page(object, ...);
>    }, list(object=as.name(title))));
>  }
> }
>
> page.default <- utils::page;
>
> page(getAnywhere("predict.smooth.spline.fit"))
>
> You can have page.function(), page.character(), page.environment(),
> etc. and make these call page.default() indirectly.  What I think
> would be a very useful add on is to add an argument 'title' for which
> you can set/override the title.  Then the "ugly" substitute() calls
> could be limited to one specific case; where a "default" object is
> passed and no title is set.
>
> If you want to, I could play around with a bit.
>
> /Henrik
>
> On 4/5/06, Kurt Hornik <Kurt.Hornik at wu-wien.ac.at> wrote:
>>>>>>> Prof Brian Ripley writes:
>>
>>> On Wed, 5 Apr 2006, Henrik Bengtsson wrote:
>>>> Hi,
>
> [snip]
>
>>> As for
>>
>>>>> PS, may I suggest to modify page() so that
>>>>> 'page(getAnywhere("predict.smooth.spline.fit"))' works? DS.
>>
>>> it is rather tricky.  page() takes a name aka symbol as its argument
>>> (and is thereby S-compatible), and also works with a bare character
>>> string (undocumented).  What you have here is a call that does not
>>> even return a function.  It is more reasonable that
>>> stats:::predict.smooth.spline.fit should work, and it is also a call.
>>> I have in the past thought about special-casing that, but it is a
>>> valid name (you would have to back-quote it, but it does work).  So
>>> one possible way out would be to use get() on a name and evaluate
>>> calls, e.g.
>>
>>> page <- function(x, method = c("dput", "print"), ...)
>>> {
>>>      subx <- substitute(x)
>>>      have_object <- FALSE
>>>      if(is.call(subx)) {
>>>          object <- x
>>>          have_object <- TRUE
>>>          subx <- deparse(subx)
>>>      } else {
>>>          if(is.character(x)) subx <- x
>>>          else if(is.name(subx)) subx <- deparse(subx)
>>>          if (!is.character(subx) || length(subx) != 1)
>>>              stop("'page' requires a name, call or character string")
>>>          parent <- parent.frame()
>>>          if(exists(subx, envir = parent, inherits=TRUE)) {
>>>              object <- get(subx, envir = parent, inherits=TRUE)
>>>              have_object <- TRUE
>>>          }
>>>      }
>>>      if(have_object) {
>>>          method <- match.arg(method)
>>>          file <- tempfile("Rpage.")
>>>          if(method == "dput")
>>>              dput(object, file)
>>>          else {
>>>              sink(file)
>>>              print(object)
>>>              sink()
>>>          }
>>>       file.show(file, title = subx, delete.file = TRUE, ...)
>>>      } else
>>>       stop(gettextf("no object named '%s' to show", subx), domain = NA)
>>> }
>>
>>> which also allows 1-element character vectors (and I am not entirely
>>> sure we want that).
>>
>> There was a similar issue with prompt() (actually, its default method)
>> for which I ended up "temporarily" providing the following (argh):
>>
>>         else {
>>             name <- substitute(object)
>>             if (is.name(name))
>>                 as.character(name)
>>             else if (is.call(name) && (as.character(name[[1]]) %in%
>>                 c("::", ":::", "getAnywhere"))) {
>>                 name <- as.character(name)
>>                 name[length(name)]
>>             }
>>             else stop("cannot determine a usable name")
>>         }
>>
>> Best
>> -k
>>
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>
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>
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595