[Rd] detect ->

[Adrian Dușa]

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
> > >
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> > 
> > ______________________________________________
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> 
> —
> 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