[Rd] detect ->

[William Dunlap]

You are right.  >= is not as evocative as =>.  Perhaps > and < would do?
%=>% and %<=% would work.
Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Wed, Apr 15, 2020 at 12:41 AM Adrian Dușa <dusa.adrian using gmail.com> wrote:

> Dear Bill,
>
> I already tried this, and it would have been great as (currently) the
> sufficiency relation is precisely "=>"... but:
>
> foo <- function(x) return(substitute(x))
> foo(A => B)
> Error: unexpected '>' in "foo(A =>"
>
> It seems that "=>" is a syntactic error for the R parser, while "<=" is
> not because it denotes less than or equal.
>
> Now, if I could find a way to define "=>" as a standalone operator, and
> convince the R parser to bypass that error, it would solve everything. If
> this is not possible, I am back to detecting "->".
>
> Best,
> Adrian
>
>
> > On 13 Apr 2020, at 19:19, William Dunlap <wdunlap using tibco.com> wrote:
> >
> > Using => and <= instead of -> and <- would make things easier, although
> the precedence would be different.
> >
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com
> >
> >
> > On Mon, Apr 13, 2020 at 1:43 AM Adrian Dușa <dusa.adrian using gmail.com>
> wrote:
> > Thank you for your replies, this actually has little to do with the
> regular R code but more to signal what in my package QCA is referred to as
> a necessity relation A <- B (A is necessary for B) and sufficiency A -> B
> (A is sufficient for B).
> >
> > If switched by the parser, A -> B becomes B <- A which makes B necessary
> for A, while the intention is to signal sufficiency for B.
> >
> > Capturing in a quoted string is trivial, but I am now experimenting with
> substitute() to allow unquoted expressions.
> >
> > This is especially useful when selecting A and B from the columns of a
> data frame, using: c(A, B) instead of c("A", "B") with a lot more quotes
> for more complex expressions using more columns.
> >
> > I would be grateful for any pointer to a project that processes the code
> while it is still raw text. I could maybe learn from their code and adapt
> to my use case.
> >
> > Best wishes,
> > Adrian
> >
> > > On 13 Apr 2020, at 11:23, Gabriel Becker <gabembecker using gmail.com>
> wrote:
> > >
> > > Adrian,
> > >
> > > Indeed, this has come up in a few places, but as Gabor says, there is
> no such thing as right hand assignment at any point after parsing is
> complete.
> > >
> > > This means the only feasible way to detect it, which a few projects do
> I believe, is process the code while it is still raw text, before it goes
> into the parser, and have clever enough regular expressions.
> > >
> > > The next question, then, is why are you trying to detect right
> assignment. Doing so can be arguably useful fo linting, its true.
> Otherwise, though, because its not really a "real thing" when the R code is
> being executed, its not something thats generally meaningful to detect in
> most cases.
> > >
> > > Best,
> > > ~G
> > >
> > > On Mon, Apr 13, 2020 at 12:52 AM Gábor Csárdi <csardi.gabor using gmail.com>
> wrote:
> > > That parser already flips -> to <- before creating the parse tree.
> > >
> > > Gabor
> > >
> > > On Mon, Apr 13, 2020 at 8:39 AM Adrian Dușa <dusa.adrian using gmail.com>
> wrote:
> > > >
> > > > I searched and tried for hours, to no avail although it looks simple.
> > > >
> > > > (function(x) substitute(x))(A <- B)
> > > > #A <- B
> > > >
> > > > (function(x) substitute(x))(A -> B)
> > > > # B <- A
> > > >
> > > > In the first example, A occurs on the LHS, but in the second example
> A is somehow evaluated as if it occured on the RHS, despite my
> understanding that substitute() returns the unevaluated parse tree.
> > > >
> > > > Is there any way, or is it even possible to detect the right hand
> assignment, to determine whether A occurs on the LHS?
> > > >
> > > > Thanks in advance for any hint,
> > > > Adrian
> > > >
> > > > —
> > > > Adrian Dusa
> > > > University of Bucharest
> > > > Romanian Social Data Archive
> > > > Soseaua Panduri nr. 90-92
> > > > 050663 Bucharest sector 5
> > > > Romania
> > > > https://adriandusa.eu
> > > >
> > > > ______________________________________________
> > > > R-devel using r-project.org mailing list
> > > > https://stat.ethz.ch/mailman/listinfo/r-devel
> > >
> > > ______________________________________________
> > > R-devel using r-project.org mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
> > —
> > Adrian Dusa
> > University of Bucharest
> > Romanian Social Data Archive
> > Soseaua Panduri nr. 90-92
> > 050663 Bucharest sector 5
> > Romania
> > https://adriandusa.eu
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> —
> Adrian Dusa
> University of Bucharest
> Romanian Social Data Archive
> Soseaua Panduri nr. 90-92
> 050663 Bucharest sector 5
> Romania
> https://adriandusa.eu
>
>

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