[Rd] capture "->"

[Dmitri Popavenko]

Hi everyone,

I am aware this is a parser issue, but is there any possibility to capture
the use of the inverse assignment operator into a formula?

Something like:

> foo <- function(x) substitute(x)

gives:

> foo(A -> B)
B <- A

I wonder if there is any possibility whatsoever to signal the use of ->
instead of <-

Thank you,
Dmitri

[[alternative HTML version deleted]]

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[Duncan Murdoch]

On 01/03/2024 4:17 a.m., Dmitri Popavenko wrote:

Hi everyone,

I am aware this is a parser issue, but is there any possibility to capture
the use of the inverse assignment operator into a formula?

Something like:


foo <- function(x) substitute(x)


gives:


foo(A -> B)

B <- A

I wonder if there is any possibility whatsoever to signal the use of ->
instead of <-


If you parse it with srcrefs, you could look at the source.  The parser 
doesn't record whether it was A -> B or B <- A anywhere else.


Duncan Murdoch

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[Dmitri Popavenko]

Dear Duncan,

On Fri, Mar 1, 2024 at 11:30 AM Duncan Murdoch 
wrote:

> ...
> If you parse it with srcrefs, you could look at the source.  The parser
> doesn't record whether it was A -> B or B <- A anywhere else.
>

Thank you, this gets me closer but it still needs a little push:

> foo <- function(x) {
  x <- substitute(x)
  return(attr(x, "srcref")[[2]])
}

> foo(A -> B)
NULL

This seems to work, however:
> foo({A -> B})
A -> B

Is there a way to treat the formula as if it was enclosed between the curly
brackets?
Dmitri

[[alternative HTML version deleted]]

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[Duncan Murdoch]

On 01/03/2024 5:25 a.m., Dmitri Popavenko wrote:

Dear Duncan,

On Fri, Mar 1, 2024 at 11:30 AM Duncan Murdoch > wrote:


...
If you parse it with srcrefs, you could look at the source.  The parser
doesn't record whether it was A -> B or B <- A anywhere else.


Thank you, this gets me closer but it still needs a little push:

 > foo <- function(x) {
   x <- substitute(x)
   return(attr(x, "srcref")[[2]])
}

 > foo(A -> B)
NULL

This seems to work, however:
 > foo({A -> B})
A -> B

Is there a way to treat the formula as if it was enclosed between the 
curly brackets?

Dmitri


I was thinking more of you doing something like

 parse(text = "A -> B", keep.source = TRUE)

I forget what the exact rules are for attaching srcrefs to arguments of 
functions, but I do remember they are a little strange, because not 
every possible argument can accept a srcref attribute.  For example, you 
can't attach one to NULL, or to a name.


Srcrefs are also fairly big and building them is slow, so I think we 
tried to limit them to where they were needed, we didn't try to attach 
them to every subexpression, just one per statement.  Each expression 
within {} is a separate statement, so we get srcrefs attached to the {. 
But in "foo(A -> B)" probably you only get one on the foo call.


In some circumstances you could get the srcref on that call by looking 
at sys.call().  But then things are complicated again, because R doesn't 
attach srcrefs to things typed at the console, only to things that are 
sourced from files or text strings (and parsed with keep.source=TRUE).


So I think you should probably require input from a string or a file, or 
not expect foo(A -> B) to work without some decoration.


Duncan Murdoch

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[Dmitri Popavenko]

On Fri, Mar 1, 2024 at 1:00 PM Duncan Murdoch 
wrote:

> ...
> I was thinking more of you doing something like
>
>   parse(text = "A -> B", keep.source = TRUE)
>
> I forget what the exact rules are for attaching srcrefs to arguments of
> functions, but I do remember they are a little strange, because not
> every possible argument can accept a srcref attribute.  For example, you
> can't attach one to NULL, or to a name.
>
> Srcrefs are also fairly big and building them is slow, so I think we
> tried to limit them to where they were needed, we didn't try to attach
> them to every subexpression, just one per statement.  Each expression
> within {} is a separate statement, so we get srcrefs attached to the {.
> But in "foo(A -> B)" probably you only get one on the foo call.
>
> In some circumstances you could get the srcref on that call by looking
> at sys.call().  But then things are complicated again, because R doesn't
> attach srcrefs to things typed at the console, only to things that are
> sourced from files or text strings (and parsed with keep.source=TRUE).
>
> So I think you should probably require input from a string or a file, or
> not expect foo(A -> B) to work without some decoration.
>

Indeed, the more challenging task is to identify "->" at the console
(from a script or a string, seems trivial now).

I would be willing to decorate as much as it takes to make this work, I am
just empty on more ideas how to persuade the parser.
Dmitri

[[alternative HTML version deleted]]

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[Duncan Murdoch]

On 01/03/2024 8:51 a.m., Dmitri Popavenko wrote:
On Fri, Mar 1, 2024 at 1:00 PM Duncan Murdoch > wrote:


...
I was thinking more of you doing something like

   parse(text = "A -> B", keep.source = TRUE)

I forget what the exact rules are for attaching srcrefs to arguments of
functions, but I do remember they are a little strange, because not
every possible argument can accept a srcref attribute.  For example,
you
can't attach one to NULL, or to a name.

Srcrefs are also fairly big and building them is slow, so I think we
tried to limit them to where they were needed, we didn't try to attach
them to every subexpression, just one per statement.  Each expression
within {} is a separate statement, so we get srcrefs attached to the {.
But in "foo(A -> B)" probably you only get one on the foo call.

In some circumstances you could get the srcref on that call by looking
at sys.call().  But then things are complicated again, because R
doesn't
attach srcrefs to things typed at the console, only to things that are
sourced from files or text strings (and parsed with keep.source=TRUE).

So I think you should probably require input from a string or a
file, or
not expect foo(A -> B) to work without some decoration.


Indeed, the more challenging task is to identify "->" at the console
(from a script or a string, seems trivial now).

I would be willing to decorate as much as it takes to make this work, I 
am just empty on more ideas how to persuade the parser.


By "decorate", I meant putting it in quotes and parsing it using 
parse(text=...), or putting it in braces as you found.  I think parsing 
a string is most likely to be reliable because someone might turn off 
`keep.source` and then the braced approach would fail.  But you have 
control over it when you call parse() yourself.


Duncan Murdoch

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[avi.e.gross]

I am wondering what the specific need for this is or is it just an exercise?

Where does it matter if a chunk of code assigns using "<-" beforehand or "->" 
after hand, or for that matter assigns indirectly without a symbol?

And whatever you come up with, will it also support the global assignment of 
"->>" as compared to ""<<-" too?

I do wonder if you can re-declare the assignment operators or would that mess 
up the parser.

-Original Message-
From: R-devel  On Behalf Of Duncan Murdoch
Sent: Friday, March 1, 2024 9:23 AM
To: Dmitri Popavenko 
Cc: r-devel 
Subject: Re: [Rd] capture "->"

On 01/03/2024 8:51 a.m., Dmitri Popavenko wrote:
> On Fri, Mar 1, 2024 at 1:00 PM Duncan Murdoch  > wrote:
> 
> ...
> I was thinking more of you doing something like
> 
>parse(text = "A -> B", keep.source = TRUE)
> 
> I forget what the exact rules are for attaching srcrefs to arguments of
> functions, but I do remember they are a little strange, because not
> every possible argument can accept a srcref attribute.  For example,
> you
> can't attach one to NULL, or to a name.
> 
> Srcrefs are also fairly big and building them is slow, so I think we
> tried to limit them to where they were needed, we didn't try to attach
> them to every subexpression, just one per statement.  Each expression
> within {} is a separate statement, so we get srcrefs attached to the {.
> But in "foo(A -> B)" probably you only get one on the foo call.
> 
> In some circumstances you could get the srcref on that call by looking
> at sys.call().  But then things are complicated again, because R
> doesn't
> attach srcrefs to things typed at the console, only to things that are
> sourced from files or text strings (and parsed with keep.source=TRUE).
> 
> So I think you should probably require input from a string or a
> file, or
> not expect foo(A -> B) to work without some decoration.
> 
> 
> Indeed, the more challenging task is to identify "->" at the console
> (from a script or a string, seems trivial now).
> 
> I would be willing to decorate as much as it takes to make this work, I 
> am just empty on more ideas how to persuade the parser.

By "decorate", I meant putting it in quotes and parsing it using 
parse(text=...), or putting it in braces as you found.  I think parsing 
a string is most likely to be reliable because someone might turn off 
`keep.source` and then the braced approach would fail.  But you have 
control over it when you call parse() yourself.

Duncan Murdoch

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[Adrian Dușa]

I would also be interested in that.
For me, this is interesting for my QCA package, over which Dmitri and I
have exchanged a couple of messages.
The "<-" operator is used to denote necessity, and the "->" is used for
sufficiency.

Users often make use of Boolean expressions such as A*B + C -> Y
(to calculate if the expression A*B + C is sufficient for the outcome Y)

The parser inverses it into Y <- A*B + C, as if the outcome Y is necessary
for the expression A*B + C, which changes the nature of the expression.

Quoting such expressions is already possible and it works as expected. We
were trying to avoid the quotes, if at all possible, to simplify the
command use in the manuals.

Best wishes,
Adrian

On Fri, Mar 1, 2024 at 4:33 PM  wrote:

> I am wondering what the specific need for this is or is it just an
> exercise?
>
> Where does it matter if a chunk of code assigns using "<-" beforehand or
> "->" after hand, or for that matter assigns indirectly without a symbol?
>
> And whatever you come up with, will it also support the global assignment
> of "->>" as compared to ""<<-" too?
>
> I do wonder if you can re-declare the assignment operators or would that
> mess up the parser.
>
> -Original Message-
> From: R-devel  On Behalf Of Duncan Murdoch
> Sent: Friday, March 1, 2024 9:23 AM
> To: Dmitri Popavenko 
> Cc: r-devel 
> Subject: Re: [Rd] capture "->"
>
> On 01/03/2024 8:51 a.m., Dmitri Popavenko wrote:
> > On Fri, Mar 1, 2024 at 1:00 PM Duncan Murdoch  > > wrote:
> >
> > ...
> > I was thinking more of you doing something like
> >
> >parse(text = "A -> B", keep.source = TRUE)
> >
> > I forget what the exact rules are for attaching srcrefs to arguments
> of
> > functions, but I do remember they are a little strange, because not
> > every possible argument can accept a srcref attribute.  For example,
> > you
> > can't attach one to NULL, or to a name.
> >
> > Srcrefs are also fairly big and building them is slow, so I think we
> > tried to limit them to where they were needed, we didn't try to
> attach
> > them to every subexpression, just one per statement.  Each expression
> > within {} is a separate statement, so we get srcrefs attached to the
> {.
> > But in "foo(A -> B)" probably you only get one on the foo call.
> >
> > In some circumstances you could get the srcref on that call by
> looking
> > at sys.call().  But then things are complicated again, because R
> > doesn't
> > attach srcrefs to things typed at the console, only to things that
> are
> > sourced from files or text strings (and parsed with
> keep.source=TRUE).
> >
> > So I think you should probably require input from a string or a
> > file, or
> > not expect foo(A -> B) to work without some decoration.
> >
> >
> > Indeed, the more challenging task is to identify "->" at the console
> > (from a script or a string, seems trivial now).
> >
> > I would be willing to decorate as much as it takes to make this work, I
> > am just empty on more ideas how to persuade the parser.
>
> By "decorate", I meant putting it in quotes and parsing it using
> parse(text=...), or putting it in braces as you found.  I think parsing
> a string is most likely to be reliable because someone might turn off
> `keep.source` and then the braced approach would fail.  But you have
> control over it when you call parse() yourself.
>
> Duncan Murdoch
>
> __
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> __
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

[[alternative HTML version deleted]]

__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Re: [Rd] capture "->"

[avi.e.gross]

Adrian,
 
That is indeed a specialized need albeit not necessarily one that cannot be 
done by requiring an alternate way of typing a formula that avoids being 
something the parser sees as needed to do at that level.
 
In this case, my other questions become moot as I assume the global assignment 
operator and somethings like assign(“xyz”, 5) will not be in the way.
 
What I was wondering about is what happens if you temporarily disable the 
meaning of the assignment operator <- and turn it back on after.
 
In the following code, for no reason, I redefine + to mean – and then undo it:
 
 
> temp <- `+`
> `+` <- `-`
> 5 + 3
[1] 2
> `+` <- temp
> 5 + 3
[1] 8
 
I have no idea if a similar technique could save and later restore the meaning 
of <- and replace it with something appropriate so that an expression using it 
is not evaluated the same way and leaves it alone long enough …
 
Of course, even if this works, it could cause side effects if anything else is 
done between changes that invokes it (maybe not likely) or the change back is 
not done perhaps due to an error interruption.
 
 
Avi
 
From: Adrian Dușa  
Sent: Friday, March 1, 2024 11:38 AM
To: avi.e.gr...@gmail.com
Cc: r-devel ; Dmitri Popavenko 

Subject: Re: [Rd] capture "->"
 
I would also be interested in that.
For me, this is interesting for my QCA package, over which Dmitri and I have 
exchanged a couple of messages.
The "<-" operator is used to denote necessity, and the "->" is used for 
sufficiency.
 
Users often make use of Boolean expressions such as A*B + C -> Y
(to calculate if the expression A*B + C is sufficient for the outcome Y)
 
The parser inverses it into Y <- A*B + C, as if the outcome Y is necessary for 
the expression A*B + C, which changes the nature of the expression.
 
Quoting such expressions is already possible and it works as expected. We were 
trying to avoid the quotes, if at all possible, to simplify the command use in 
the manuals.
 
Best wishes,
Adrian
 
On Fri, Mar 1, 2024 at 4:33 PM mailto:avi.e.gr...@gmail.com> > wrote:
I am wondering what the specific need for this is or is it just an exercise?

Where does it matter if a chunk of code assigns using "<-" beforehand or "->" 
after hand, or for that matter assigns indirectly without a symbol?

And whatever you come up with, will it also support the global assignment of 
"->>" as compared to ""<<-" too?

I do wonder if you can re-declare the assignment operators or would that mess 
up the parser.

-Original Message-
From: R-devel mailto:r-devel-boun...@r-project.org> > On Behalf Of Duncan Murdoch
Sent: Friday, March 1, 2024 9:23 AM
To: Dmitri Popavenko mailto:dmitri.popave...@gmail.com> >
Cc: r-devel mailto:r-devel@r-project.org> >
Subject: Re: [Rd] capture "->"

On 01/03/2024 8:51 a.m., Dmitri Popavenko wrote:
> On Fri, Mar 1, 2024 at 1:00 PM Duncan Murdoch    
>  >> wrote:
> 
> ...
> I was thinking more of you doing something like
> 
>parse(text = "A -> B", keep.source = TRUE)
> 
> I forget what the exact rules are for attaching srcrefs to arguments of
> functions, but I do remember they are a little strange, because not
> every possible argument can accept a srcref attribute.  For example,
> you
> can't attach one to NULL, or to a name.
> 
> Srcrefs are also fairly big and building them is slow, so I think we
> tried to limit them to where they were needed, we didn't try to attach
> them to every subexpression, just one per statement.  Each expression
> within {} is a separate statement, so we get srcrefs attached to the {.
> But in "foo(A -> B)" probably you only get one on the foo call.
> 
> In some circumstances you could get the srcref on that call by looking
> at sys.call().  But then things are complicated again, because R
> doesn't
> attach srcrefs to things typed at the console, only to things that are
> sourced from files or text strings (and parsed with keep.source=TRUE).
> 
> So I think you should probably require input from a string or a
> file, or
> not expect foo(A -> B) to work without some decoration.
> 
> 
> Indeed, the more challenging task is to identify "->" at the console
> (from a script or a string, seems trivial now).
> 
> I would be willing to decorate as much as it takes to make this work, I 
> am just empty on more ideas how to persuade the parser.

By "decorate", I meant putting it in quotes and parsing it using 
parse(text=...), or putting it in braces as you found.  I think parsing 
a string is most likely to be reliable because someone might turn off 
`keep.source` and then the braced approach would fail.  But you have 
control over it when you call parse() yourself.

Duncan Murdoch

__
R-devel@r-project.org   mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel