Re: [Rd] brief update on the pipe operator in R-devel
If
3 |> x => f(x, y=x)
were allowed then I think that
runif(1) |> x => f(x, y=x)
be parsed as
f(runif(1), y=runif(1))
so runif(1) would be evaluated twice, leading to incorrect results from f().
-Bill
On Fri, Jan 15, 2021 at 2:16 PM Avi Gross via R-devel
wrote:
> Gabor,
>
> Although it might be nice if all imagined cases worked, there are many
> ways to work around and get the results you want.
>
> You may want to consider that it is easier to recognize the symbol you use
> (x in the examples) if it is alone and used only exactly once and it the
> list of function arguments. If you want the x used multiple times, you can
> make a function that accepts the x once and then invokes another function
> and reuses the x as often as needed. Similarly for 1+x.
>
> I do not know if the above choice was made to make it easier and faster to
> apply the above, or to avoid possible bad edge cases. Have you tested other
> ideas like:
>
> 3 |> x => f(x=5)
> Or
> 3 |> x => f(x, y=x)
>
> I mean ones where a default is supplied, not that it makes much sense here?
>
> I am thinking of the concept of substitution as is often done for text or
> symbols. Often the substitution is done for the first instance found unless
> you specify you want a global change. In your examples, if only the first
> use of x would be replaced, the second naked x being left alone would be an
> error. If all instances were changed, what anomalies might happen? Giving a
> vector of length 1 containing the number 3 seems harmless enough to
> duplicate. But the pipeline can send all kinds of interesting data
> structures through including data.frames and arbitrary objects.
>
>
> -Original Message-
> From: R-devel On Behalf Of Gabor
> Grothendieck
> Sent: Friday, January 15, 2021 7:28 AM
> To: Tierney, Luke
> Cc: R-devel@r-project.org
> Subject: Re: [Rd] brief update on the pipe operator in R-devel
>
> These are documented but still seem like serious deficiencies:
>
> > f <- function(x, y) x + 10*y
> > 3 |> x => f(x, x)
> Error in f(x, x) : pipe placeholder may only appear once
>
> > 3 |> x => f(1+x, 1)
> Error in f(1 + x, 1) :
> pipe placeholder must only appear as a top-level argument in the RHS call
>
> Also note:
>
> ?"=>"
> No documentation for ‘=>’ in specified packages and libraries:
> you could try ‘??=>’
>
> On Tue, Dec 22, 2020 at 5:28 PM wrote:
> >
> > It turns out that allowing a bare function expression on the
> > right-hand side (RHS) of a pipe creates opportunities for confusion
> > and mistakes that are too risky. So we will be dropping support for
> > this from the pipe operator.
> >
> > The case of a RHS call that wants to receive the LHS result in an
> > argument other than the first can be handled with just implicit first
> > argument passing along the lines of
> >
> > mtcars |> subset(cyl == 4) |> (\(d) lm(mpg ~ disp, data = d))()
> >
> > It was hoped that allowing a bare function expression would make this
> > more convenient, but it has issues as outlined below. We are exploring
> > some alternatives, and will hopefully settle on one soon after the
> > holidays.
> >
> > The basic problem, pointed out in a comment on Twitter, is that in
> > expressions of the form
> >
> > 1 |> \(x) x + 1 -> y
> > 1 |> \(x) x + 1 |> \(y) x + y
> >
> > everything after the \(x) is parsed as part of the body of the
> > function. So these are parsed along the lines of
> >
> > 1 |> \(x) { x + 1 -> y }
> > 1 |> \(x) { x + 1 |> \(y) x + y }
> >
> > In the first case the result is assigned to a (useless) local
> > variable. Someone writing this is more likely to have intended to
> > assign the result to a global variable, as this would:
> >
> > (1 |> \(x) x + 1) -> y
> >
> > In the second case the 'x' in 'x + y' refers to the local variable 'x'
> > in the first RHS function. Someone writing this is more likely to have
> > meant
> >
> > (1 |> \(x) x + 1) |> \(y) x + y
> >
> > with 'x' in 'x + y' now referring to a global variable:
> >
> > > x <- 2
> > > 1 |> \(x) x + 1 |> \(y) x + y
> > [1] 3
> > > (1 |> \(x) x + 1) |> \(y) x + y
> > [1] 4
> >
> > These issues arise with any approach in R that allows a bare function
> > expression on the RHS of a pipe operation. It also arises in other
> > languages with pipe operators. For example, here is the
Re: [Rd] brief update on the pipe operator in R-devel
Gabor,
Although it might be nice if all imagined cases worked, there are many ways to
work around and get the results you want.
You may want to consider that it is easier to recognize the symbol you use (x
in the examples) if it is alone and used only exactly once and it the list of
function arguments. If you want the x used multiple times, you can make a
function that accepts the x once and then invokes another function and reuses
the x as often as needed. Similarly for 1+x.
I do not know if the above choice was made to make it easier and faster to
apply the above, or to avoid possible bad edge cases. Have you tested other
ideas like:
3 |> x => f(x=5)
Or
3 |> x => f(x, y=x)
I mean ones where a default is supplied, not that it makes much sense here?
I am thinking of the concept of substitution as is often done for text or
symbols. Often the substitution is done for the first instance found unless you
specify you want a global change. In your examples, if only the first use of x
would be replaced, the second naked x being left alone would be an error. If
all instances were changed, what anomalies might happen? Giving a vector of
length 1 containing the number 3 seems harmless enough to duplicate. But the
pipeline can send all kinds of interesting data structures through including
data.frames and arbitrary objects.
-Original Message-
From: R-devel On Behalf Of Gabor Grothendieck
Sent: Friday, January 15, 2021 7:28 AM
To: Tierney, Luke
Cc: R-devel@r-project.org
Subject: Re: [Rd] brief update on the pipe operator in R-devel
These are documented but still seem like serious deficiencies:
> f <- function(x, y) x + 10*y
> 3 |> x => f(x, x)
Error in f(x, x) : pipe placeholder may only appear once
> 3 |> x => f(1+x, 1)
Error in f(1 + x, 1) :
pipe placeholder must only appear as a top-level argument in the RHS call
Also note:
?"=>"
No documentation for ‘=>’ in specified packages and libraries:
you could try ‘??=>’
On Tue, Dec 22, 2020 at 5:28 PM wrote:
>
> It turns out that allowing a bare function expression on the
> right-hand side (RHS) of a pipe creates opportunities for confusion
> and mistakes that are too risky. So we will be dropping support for
> this from the pipe operator.
>
> The case of a RHS call that wants to receive the LHS result in an
> argument other than the first can be handled with just implicit first
> argument passing along the lines of
>
> mtcars |> subset(cyl == 4) |> (\(d) lm(mpg ~ disp, data = d))()
>
> It was hoped that allowing a bare function expression would make this
> more convenient, but it has issues as outlined below. We are exploring
> some alternatives, and will hopefully settle on one soon after the
> holidays.
>
> The basic problem, pointed out in a comment on Twitter, is that in
> expressions of the form
>
> 1 |> \(x) x + 1 -> y
> 1 |> \(x) x + 1 |> \(y) x + y
>
> everything after the \(x) is parsed as part of the body of the
> function. So these are parsed along the lines of
>
> 1 |> \(x) { x + 1 -> y }
> 1 |> \(x) { x + 1 |> \(y) x + y }
>
> In the first case the result is assigned to a (useless) local
> variable. Someone writing this is more likely to have intended to
> assign the result to a global variable, as this would:
>
> (1 |> \(x) x + 1) -> y
>
> In the second case the 'x' in 'x + y' refers to the local variable 'x'
> in the first RHS function. Someone writing this is more likely to have
> meant
>
> (1 |> \(x) x + 1) |> \(y) x + y
>
> with 'x' in 'x + y' now referring to a global variable:
>
> > x <- 2
> > 1 |> \(x) x + 1 |> \(y) x + y
> [1] 3
> > (1 |> \(x) x + 1) |> \(y) x + y
> [1] 4
>
> These issues arise with any approach in R that allows a bare function
> expression on the RHS of a pipe operation. It also arises in other
> languages with pipe operators. For example, here is the last example
> in Julia:
>
> julia> x = 2
> 2
> julia> 1 |> x -> x + 1 |> y -> x + y
> 3
> julia> ( 1 |> x -> x + 1 ) |> y -> x + y
> 4
>
> Even though proper use of parentheses can work around these issues,
> the likelihood of making mistakes that are hard to track down is too
> high. So we will disallow the use of bare function expressions on the
> right hand side of a pipe.
>
> Best,
>
> luke
>
> --
> Luke Tierney
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa Phone: 319-335-3386
> Department of Statistics andFax: 319-335-3017
> Actuarial Science
>
Re: [Rd] brief update on the pipe operator in R-devel
These are documented but still seem like serious deficiencies:
> f <- function(x, y) x + 10*y
> 3 |> x => f(x, x)
Error in f(x, x) : pipe placeholder may only appear once
> 3 |> x => f(1+x, 1)
Error in f(1 + x, 1) :
pipe placeholder must only appear as a top-level argument in the RHS call
Also note:
?"=>"
No documentation for ‘=>’ in specified packages and libraries:
you could try ‘??=>’
On Tue, Dec 22, 2020 at 5:28 PM wrote:
>
> It turns out that allowing a bare function expression on the
> right-hand side (RHS) of a pipe creates opportunities for confusion
> and mistakes that are too risky. So we will be dropping support for
> this from the pipe operator.
>
> The case of a RHS call that wants to receive the LHS result in an
> argument other than the first can be handled with just implicit first
> argument passing along the lines of
>
> mtcars |> subset(cyl == 4) |> (\(d) lm(mpg ~ disp, data = d))()
>
> It was hoped that allowing a bare function expression would make this
> more convenient, but it has issues as outlined below. We are exploring
> some alternatives, and will hopefully settle on one soon after the
> holidays.
>
> The basic problem, pointed out in a comment on Twitter, is that in
> expressions of the form
>
> 1 |> \(x) x + 1 -> y
> 1 |> \(x) x + 1 |> \(y) x + y
>
> everything after the \(x) is parsed as part of the body of the
> function. So these are parsed along the lines of
>
> 1 |> \(x) { x + 1 -> y }
> 1 |> \(x) { x + 1 |> \(y) x + y }
>
> In the first case the result is assigned to a (useless) local
> variable. Someone writing this is more likely to have intended to
> assign the result to a global variable, as this would:
>
> (1 |> \(x) x + 1) -> y
>
> In the second case the 'x' in 'x + y' refers to the local variable 'x'
> in the first RHS function. Someone writing this is more likely to have
> meant
>
> (1 |> \(x) x + 1) |> \(y) x + y
>
> with 'x' in 'x + y' now referring to a global variable:
>
> > x <- 2
> > 1 |> \(x) x + 1 |> \(y) x + y
> [1] 3
> > (1 |> \(x) x + 1) |> \(y) x + y
> [1] 4
>
> These issues arise with any approach in R that allows a bare function
> expression on the RHS of a pipe operation. It also arises in other
> languages with pipe operators. For example, here is the last example
> in Julia:
>
> julia> x = 2
> 2
> julia> 1 |> x -> x + 1 |> y -> x + y
> 3
> julia> ( 1 |> x -> x + 1 ) |> y -> x + y
> 4
>
> Even though proper use of parentheses can work around these issues,
> the likelihood of making mistakes that are hard to track down is too
> high. So we will disallow the use of bare function expressions on the
> right hand side of a pipe.
>
> Best,
>
> luke
>
> --
> Luke Tierney
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa Phone: 319-335-3386
> Department of Statistics andFax: 319-335-3017
> Actuarial Science
> 241 Schaeffer Hall email: luke-tier...@uiowa.edu
> Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
>
> __
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
--
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
[Rd] brief update on the pipe operator in R-devel
It turns out that allowing a bare function expression on the
right-hand side (RHS) of a pipe creates opportunities for confusion
and mistakes that are too risky. So we will be dropping support for
this from the pipe operator.
The case of a RHS call that wants to receive the LHS result in an
argument other than the first can be handled with just implicit first
argument passing along the lines of
mtcars |> subset(cyl == 4) |> (\(d) lm(mpg ~ disp, data = d))()
It was hoped that allowing a bare function expression would make this
more convenient, but it has issues as outlined below. We are exploring
some alternatives, and will hopefully settle on one soon after the
holidays.
The basic problem, pointed out in a comment on Twitter, is that in
expressions of the form
1 |> \(x) x + 1 -> y
1 |> \(x) x + 1 |> \(y) x + y
everything after the \(x) is parsed as part of the body of the
function. So these are parsed along the lines of
1 |> \(x) { x + 1 -> y }
1 |> \(x) { x + 1 |> \(y) x + y }
In the first case the result is assigned to a (useless) local
variable. Someone writing this is more likely to have intended to
assign the result to a global variable, as this would:
(1 |> \(x) x + 1) -> y
In the second case the 'x' in 'x + y' refers to the local variable 'x'
in the first RHS function. Someone writing this is more likely to have
meant
(1 |> \(x) x + 1) |> \(y) x + y
with 'x' in 'x + y' now referring to a global variable:
> x <- 2
> 1 |> \(x) x + 1 |> \(y) x + y
[1] 3
> (1 |> \(x) x + 1) |> \(y) x + y
[1] 4
These issues arise with any approach in R that allows a bare function
expression on the RHS of a pipe operation. It also arises in other
languages with pipe operators. For example, here is the last example
in Julia:
julia> x = 2
2
julia> 1 |> x -> x + 1 |> y -> x + y
3
julia> ( 1 |> x -> x + 1 ) |> y -> x + y
4
Even though proper use of parentheses can work around these issues,
the likelihood of making mistakes that are hard to track down is too
high. So we will disallow the use of bare function expressions on the
right hand side of a pipe.
Best,
luke
--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics andFax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
__
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
