[R] formula argument evaluation

[William Dunlap]

%=>% would have precendence ('order of operations') problems also.

   A + B %=>% C

is equivalent to

  A + ( B %=>% C)

and I don't think that is what you want.

as.list(quote(A + B %=>% C)) shows the first branch in the parse tree.  The
following function, str.language, shows the entire parse tree, as in

  > str.language(quote(A + B %=>% C))
  `quote(A + B %=>% C)` call(3): A + B %=>% C
    `` name(1): +
    `` name(1): A
    `` call(3): B %=>% C
      `` name(1): %=>%
      `` name(1): B
      `` name(1): C

str.language <-
function (object, ..., level = 0, name = myDeparse(substitute(object)))
{
    abbr <- function(string, maxlen = 25) {
        if (length(string) > 1 || nchar(string) > maxlen)
            paste(substring(string[1], 1, maxlen), "...", sep = "")
        else string
    }
    myDeparse <- function(object) {
        if (!is.environment(object)) {
            deparse(object)
        }
        else {
            ename <- environmentName(object)
            if (ename == "")
                ename <- "<unnamed env>"
            paste(sep = "", "<", ename, "> ", paste(collapse = " ",
                objects(object)))
        }
    }
    cat(rep("  ", level), sep = "")
    if (is.null(name))
        name <- ""
    cat(sprintf("`%s` %s(%d): %s\n", abbr(name), class(object),
        length(object), abbr(myDeparse(object))))
    a <- attributes(object)
    if (is.recursive(object) && !is.environment(object)) {
        object <- as.list(object)
        names <- names(object)
        for (i in seq_along(object)) {
            str.language(object[[i]], ..., level = level + 1,
                name = names[i])
        }
    }
    a$names <- NULL
    if (length(a) > 0) {
        str.language(a, level = level + 1, name = paste("Attributes of",
            abbr(name)))
    }
}



Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Apr 12, 2016 at 11:59 PM, Adrian Dușa <dusa.adrian at unibuc.ro> wrote:

> I suppose it would work, although "=>" is rather a descriptive symbol and
> less a function.
> But choosing between quoting:
> "A + B => C"
> and a regular function:
> A + B %=>% C
> probably quoting is the most straightforward, as the result of the foo()
> function has to be a string anyways (which is parsed by other functions).
>
> On Tue, Apr 12, 2016 at 6:20 PM, Richard M. Heiberger <rmh at temple.edu>
> wrote:
>
> > Would making it regular function %=>%, using "%" instead of quotes,
> > work for you?
> >
> > On Tue, Apr 12, 2016 at 11:09 AM, Adrian Dușa <dusa.adrian at unibuc.ro>
> > wrote:
> > > On Tue, Apr 12, 2016 at 2:08 PM, Duncan Murdoch <
> > murdoch.duncan at gmail.com>
> > > wrote:
> > >> [...]
> > >>
> > >> It never gets to evaluating it.  It is not a legal R statement, so the
> > > parser signals an error.
> > >> If you want to pass arbitrary strings to a function, you need to put
> > them
> > > in quotes.
> > >
> > > I see. I thought it was parsed inside the function, but if it's parsed
> > > before then quoting is the only option.
> > >
> > >
> > > To Keith: no, I mean it like this "A + B => C" which is translated as:
> > > "the union of A and B is sufficient for C" in set theoretic language.
> > >
> > > The "=>" operator means sufficiency, while "<=" means necessity.
> Quoting
> > > the expression is good enough, I was just curious if the quotes could
> be
> > > made redundant, somehow.
> > >
> > > Thank you both,
> > > Adrian
> > >
> > > --
> > > Adrian Dusa
> > > University of Bucharest
> > > Romanian Social Data Archive
> > > Soseaua Panduri nr.90
> > > 050663 Bucharest sector 5
> > > Romania
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
> > > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
>
> --
> Adrian Dusa
> University of Bucharest
> Romanian Social Data Archive
> Soseaua Panduri nr.90
> 050663 Bucharest sector 5
> Romania
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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