New pipe operator
First, one comment:
You're right about the illegality of _PIPE_ as a name, I had
misremembered the rule.
About your proposal:
I don't find it attractive, but I can see that some people would. But I
don't think it's necessary to put it into the base parser. Other than
using an illegal name, there doesn't seem to be a reason you couldn't
write a small function to convert your placeholder proposal to a call to
a function. So instead of typing
x |> { y <- _PIPE_+1; _PIPE_ / y }
you would type
x |> forpipe({ y <- PIPE_+1; PIPE_ / y })
I don't think "forpipe" is the right name here. I proposed a generic
"as.call" before, but I don't like that one either. I'm still trying to
think of a good name, and whether or not it makes sense for it to be
generic.
But the point is that we don't need to choose just one from all the
proposed replacements for anonymous function syntax, we can try them out
and see which ones we like. We might end up with more than one (like we
have at least 4 different high level graphics paradigms!), and that's
not the end of the world.
Duncan Murdoch
On 08/12/2020 4:26 p.m., Bravington, Mark (Data61, Hobart) wrote:
On 06/12/2020 8:22 p.m., Bravington, Mark (Data61, Hobart) wrote:
(and Duncan Murdoch responded, as below)
It still seems to me that placeholders are viable and unambiguous (only as things in RHS of pipes), and that something like
x |> foo( _PIPE_)
x |> bah( otherarg, _PIPE_)
x |> { y <- _PIPE_+1; _PIPE_ / y } # anonymous function
would be a viable solution that doesn't break syntax. This suggestion expands slightly on my previous post, to deal with anonymous functions without either ugly or cumbersome syntax. Specifically, the parser could expand curly-braces in a pipe RHS like this:
x |> {expr}
into
_ANON_( _PIPE_, {expr})( x)
where '_ANON_' itself constructs-and-calls a function with one argument called '_PIPE_' whose body consists of 'expr' (which presumably refers to '_PIPE_')
No new weird operators like \(, and the only break with normal syntax is the expansion of curly-braces--- plus treating one symbol, _PIPE_ or any other pre-agreed one perhaps even just _, as a legal name inside a pipe.
Now back to my previous post and responding to Duncan's comments:
- I don't see the problem with a placeholder--- doesn't it remove all ambiguity? Sure there needs to be a standard unclashable name and people can argue about what that should be, but the following seems clear and flexible... to me, anyway:
thing |>
foo( _PIPE_) |> # standard
bah( arg1, _PIPE_) |> # multi-arg function
_ANON_({ x <- sum( _PIPE_); _PIPE_/x + x/_PIPE_ }) # anon function
where '_PIPE_' is the ordained name of the placeholder, and '_ANON_' constructs-and-calls a function with single argument '_PIPE_'. There is just one rule (I think...): each pipe-stage must be a *call* involving the argument '_PIPE_'.
and (see end) I think the line with _ANON_ above could in fact just be
... |> { x <- sum( _PIPE_); _PIPE_/x + x/_PIPE_ }
I believe there's no ambiguity if the placeholder is *only* allowed in the RHS of a pipe expression.
Yes--- that's my suggestion: there and only there. Hence an otherwise-illegal name like _PIPE_.
I think the ambiguity arises if you allow the same syntax to be used to generate anonymous functions.
Agreed; don't allow that outside of pipes.
We can't use _PIPE_ as the placeholder, because it's a legal name.
Surely _PIPE_ is not a legal R name though? Not in my R4.1.0dev, anyway. Of course, the parser can _make_ it legal *only* in the context of RHS of pipe. Anyway, I'm not suggesting the names must be _PIPE_ and _ANON_--- the name is secondary to the concept.
But we could use _.
Yes, any unclashable name would do--- though "_" is hard to read (as per complaints about "." as placeholder, which I use in my own code). And I remember back when R decided to disallow "_" as an assignment operator. Which forced me to change about 50000 lines of code that wasn't stored in text files, so I wasn't happy--- and the only reason that was ever given to me, was "it's ugly" ! Which is kinda true.
However, implementing this makes the parser pretty ugly: its handling of _ depends on the outer context.
That context issue is already the case under the current proposal though; eg 'head(10)' in x |> head(10) # really head( <arg>, 10) or indeed 'head' in x |> head # actually a call to head(<arg>), not a symbol
I now agree that leaving out placeholder syntax was the right decision.
Others are not so sure! Re operator precedence: thanks for pointing that out, I accept that R's current operator-precedence rules make it impossible for people to cleanly implement their own preferred homemade %my_pipe_op%. All the more reason to be careful with the pipe syntax choice for base-R, of course...
Then
x |> (_ + 1) + mean(_)
could expand unambiguously to
(function(_) (_ + 1) + mean(_))(x)
but
(_ + 1) + mean(_)
shouldn't be taken to be an anonymous function declaration, otherwise things like
mean(_ |> _)
do become ambiguous: is the second placeholder the argument to the anon function, or is it the placeholder for the embedded pipe?
That wouldn't be allowed in my proposal; the "_ |> _" is illegal because the RHS is not a call. For the whole thing, I'd require
x |> _ANON_((_PIPE_ + 1) + mean( _PIPE_))
or the just-curly version
x |> { (_PIPE_ + 1) + mean( _PIPE_)}
but with the implication that this would parse out to
(`_ANON_`( { (_PIPE_ + 1) + mean( _PIPE_)}))( x)
[*] Definition of _ANON_ could be something like this--- almost certainly won't work as-is, this is just to point out that it could be done in standard R.
`_ANON_` <- function( expr) {
#1. Construct a function with arg '_PIPE_' and body 'expr'
#2. Construct a call() to that function
#3. Do the call
f <- function( `_PIPE_`) NULL body( f) <- expr environment( f) <- parent.frame() # or something... yes these details are almost certainly wrong expr2 <- substitute( f( `_PIPE_`)) # or something... eval.parent( expr2) # or something... }
Mark Bravington CSIRO Marine Lab Hobart Australia
________________________________________
From: Duncan Murdoch <murdoch.duncan at gmail.com>
Sent: Monday, 7 December 2020 21:31
To: Bravington, Mark (Data61, Hobart); Gabor Grothendieck; Gabriel Becker
Cc: r-devel at r-project.org
Subject: Re: [Rd] New pipe operator
On 06/12/2020 8:22 p.m., Bravington, Mark (Data61, Hobart) wrote:
Seems like this *could* be a good thing, and thanks to R core for considering it. But, FWIW:
- I agree with Gabor G that consistency of "syntax" should be paramount here. Enough problems have been caused by earlier superficially-convenient non-standard features in R. In particular:
-- there should not be any discrepancy between an in-place function-definition, and a predefined function attached to a symbol (as per Gabor's point).
-- Hence, the ability to say x |> foo ie without parentheses, seems bound to lead to inconsistency, because x |> foo is allowed, x |> base::foo isn't allowed without tricks, but x |> function( y) foo( y) isn't... So, x |> foo is not worth keeping. Parentheses are a price well worth paying.
-- it is still inconsistent and confusing to (apparently) invoke a function in some places--- normally--- via 'foo(x)', yet in others--- pipily--- via 'foo()'. Especially if 'foo' already has a default value for its first argument.
- I don't see the problem with a placeholder--- doesn't it remove all ambiguity? Sure there needs to be a standard unclashable name and people can argue about what that should be, but the following seems clear and flexible... to me, anyway:
thing |>
foo( _PIPE_) |> # standard
bah( arg1, _PIPE_) |> # multi-arg function
_ANON_({ x <- sum( _PIPE_); _PIPE_/x + x/_PIPE_ }) # anon function
where '_PIPE_' is the ordained name of the placeholder, and '_ANON_' constructs-and-calls a function with single argument '_PIPE_'. There is just one rule (I think...): each pipe-stage must be a *call* involving the argument '_PIPE_'.
I believe there's no ambiguity if the placeholder is *only* allowed in
the RHS of a pipe expression. I think the ambiguity arises if you allow
the same syntax to be used to generate anonymous functions. We can't
use _PIPE_ as the placeholder, because it's a legal name. But we could
use _. Then
x |> (_ + 1) + mean(_)
could expand unambiguously to
(function(_) (_ + 1) + mean(_))(x)
but
(_ + 1) + mean(_)
shouldn't be taken to be an anonymous function declaration, otherwise
things like
mean(_ |> _)
do become ambiguous: is the second placeholder the argument to the anon
function, or is it the placeholder for the embedded pipe?
However, implementing this makes the parser pretty ugly: its handling
of _ depends on the outer context. I now agree that leaving out
placeholder syntax was the right decision.
- The proposed anonymous-function syntax looks quite ugly to me, diminishing readability and inviting errors. The new pipe symbol |> already looks scarily like quantum mechanics; adding \( just puts fishbones into the symbolic soup.
- IMO it's not worth going too far to try to lure magritter-etc fans to swap to the new; my experience is that many people keep using older inferior R syntax for years after better replacements become available (even if they are aware of replacements), for various reasons. Just provide a good framework, and let nature take its course.
- Disclaimer: personally I'm not much of a pipehead anyway, so maybe I'm not the audience. But if I was to consider piping, I wouldn't be very tempted by the current proposal. OTOH, I might even be tempted to write--- and use!--- my own version of '%|>%' as above (maybe someone already has). And if R did it for me, that'd be great :)
Yours would suffer one of the same problems as magrittr's: it has the
wrong operator precedence. The current precedence ordering (from
?Syntax) is, from highest to lowest:
:: ::: access variables in a namespace
$ @ component / slot extraction
[ [[ indexing
^ exponentiation (right to left)
- + unary minus and plus
: sequence operator
%any% special operators (including %% and %/%)
* / multiply, divide
+ - (binary) add, subtract
< > <= >= == != ordering and comparison
! negation
& && and
| || or
~ as in formulae
-> ->> rightwards assignment
<- <<- assignment (right to left)
= assignment (right to left)
? help (unary and binary)
The %>% operator has higher precedence than the arithmetic operators, so
x*y %>% f()
is equivalent to x*f(y), not
f(x*y)
as it should "obviously" be. I believe the new |> operator falls
between "| ||" and "~", so
x || y |> f()
is the same as f(x || y), and
x ~ y |> f()
is x ~ f(y). There could be arguments about where the new one appears
(and there probably have been), but *clearly* magrittr's precedence is
wrong, and yours would be too, because they are both fixed at the quite
high precedence given to %any%.
Duncan Murdoch
[*] Definition of _ANON_ could be something like this--- almost certainly won't work as-is, this is just to point out that it could be done in standard R.
`_ANON_` <- function( expr) {
#1. Construct a function with arg '_PIPE_' and body 'expr'
#2. Construct a call() to that function
#3. Do the call
f <- function( `_PIPE_`) NULL
body( f) <- expr
environment( f) <- parent.frame() # or something... yes these details are almost certainly wrong
expr2 <- substitute( f( `_PIPE_`)) # or something...
eval.parent( expr2) # or something...
}
cheers
Mark
Mark Bravington
CSIRO Marine Lab
Hobart
Australia
________________________________________
From: R-devel <r-devel-bounces at r-project.org> on behalf of Gabor Grothendieck <ggrothendieck at gmail.com>
Sent: Monday, 7 December 2020 10:21
To: Gabriel Becker
Cc: r-devel at r-project.org
Subject: Re: [Rd] New pipe operator
I understand very well that it is implemented at the syntax level;
however, in any case the implementation is irrelevant to the principles.
Here a similar example to the one I gave before but this time written out:
This works:
3 |> function(x) x + 1
but this does not:
foo <- function(x) x + 1
3 |> foo
so it breaks the principle of functions being first class objects. foo and its
definition are not interchangeable. You have
to write 3 |> foo() but don't have to write 3 |> (function(x) x + 1)().
This isn't just a matter of notation, i.e. foo vs foo(), but is a
matter of breaking
the way R works as a functional language with first class functions.
On Sun, Dec 6, 2020 at 4:06 PM Gabriel Becker <gabembecker at gmail.com> wrote:
Hi Gabor,
On Sun, Dec 6, 2020 at 12:52 PM Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
I think the real issue here is that functions are supposed to be
first class objects in R
or are supposed to be and |> would break that if if is possible
to write function(x) x + 1 on the RHS but not foo (assuming foo
was defined as that function).
I don't think getting experience with using it can change that
inconsistency which seems serious to me and needs to
be addressed even if it complicates the implementation
since it drives to the heart of what R is.
With respect I think this is a misunderstanding of what is happening here.
Functions are first class citizens. |> is, for all intents and purposes, a macro.
LHS |> RHS(arg2=5)
parses to
RHS(LHS, arg2 = 5)
There are no functions at the point in time when the pipe transformation happens, because no code has been evaluated. To know if a symbol is going to evaluate to a function requires evaluation which is a step entirely after the one where the |> pipe is implemented.
Another way to think about it is that
LHS |> RHS(arg2 = 5)
is another way of writing RHS(LHS, arg2 = 5), NOT R code that is (or even can be) evaluated.
Now this is a subtle point that only really has implications in as much as it is not the case for magrittr pipes, but its relevant for discussions like this, I think.
~G
On Sat, Dec 5, 2020 at 1:08 PM Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
The construct utils::head is not that common but bare functions are
very common and to make it harder to use the common case so that
the uncommon case is slightly easier is not desirable.
Also it is trivial to write this which does work:
mtcars %>% (utils::head)
On Sat, Dec 5, 2020 at 11:59 AM Hugh Parsonage <hugh.parsonage at gmail.com> wrote:
I'm surprised by the aversion to
mtcars |> nrow
over
mtcars |> nrow()
and I think the decision to disallow the former should be
reconsidered. The pipe operator is only going to be used when the rhs
is a function, so there is no ambiguity with omitting the parentheses.
If it's disallowed, it becomes inconsistent with other treatments like
sapply(mtcars, typeof) where sapply(mtcars, typeof()) would just be
noise. I'm not sure why this decision was taken
If the only issue is with the double (and triple) colon operator, then
ideally `mtcars |> base::head` should resolve to `base::head(mtcars)`
-- in other words, demote the precedence of |>
Obviously (looking at the R-Syntax branch) this decision was
considered, put into place, then dropped, but I can't see why
precisely.
Best,
Hugh.
On Sat, 5 Dec 2020 at 04:07, Deepayan Sarkar <deepayan.sarkar at gmail.com> wrote:
On Fri, Dec 4, 2020 at 7:35 PM Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
On 04/12/2020 8:13 a.m., Hiroaki Yutani wrote:
Error: function '::' not supported in RHS call of a pipe
To me, this error looks much more friendly than magrittr's error.
Some of them got too used to specify functions without (). This
is OK until they use `::`, but when they need to use it, it takes
hours to figure out why
mtcars %>% base::head
#> Error in .::base : unused argument (head)
won't work but
mtcars %>% head
works. I think this is a too harsh lesson for ordinary R users to
learn `::` is a function. I've been wanting for magrittr to drop the
support for a function name without () to avoid this confusion,
so I would very much welcome the new pipe operator's behavior.
Thank you all the developers who implemented this!
I agree, it's an improvement on the corresponding magrittr error.
I think the semantics of not evaluating the RHS, but treating the pipe
as purely syntactical is a good decision.
I'm not sure I like the recommended way to pipe into a particular argument:
mtcars |> subset(cyl == 4) |> \(d) lm(mpg ~ disp, data = d)
or
mtcars |> subset(cyl == 4) |> function(d) lm(mpg ~ disp, data = d)
both of which are equivalent to
mtcars |> subset(cyl == 4) |> (function(d) lm(mpg ~ disp, data = d))()
It's tempting to suggest it should allow something like
mtcars |> subset(cyl == 4) |> lm(mpg ~ disp, data = .)
Which is really not that far off from
mtcars |> subset(cyl == 4) |> \(.) lm(mpg ~ disp, data = .)
once you get used to it.
One consequence of the implementation is that it's not clear how
multiple occurrences of the placeholder would be interpreted. With
magrittr,
sort(runif(10)) %>% ecdf(.)(.)
## [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
This is probably what you would expect, if you expect it to work at all, and not
ecdf(sort(runif(10)))(sort(runif(10)))
There would be no such ambiguity with anonymous functions
sort(runif(10)) |> \(.) ecdf(.)(.)
-Deepayan
which would be expanded to something equivalent to the other versions:
but that makes it quite a bit more complicated. (Maybe _ or \. should
be used instead of ., since those are not legal variable names.)
I don't think there should be an attempt to copy magrittr's special
casing of how . is used in determining whether to also include the
previous value as first argument.
Duncan Murdoch
Best,
Hiroaki Yutani
2020?12?4?(?) 20:51 Duncan Murdoch <murdoch.duncan at gmail.com>:
Just saw this on the R-devel news:
R now provides a simple native pipe syntax ?|>? as well as a shorthand
notation for creating functions, e.g. ?\(x) x + 1? is parsed as
?function(x) x + 1?. The pipe implementation as a syntax transformation
was motivated by suggestions from Jim Hester and Lionel Henry. These
features are experimental and may change prior to release.
This is a good addition; by using "|>" instead of "%>%" there should be
a chance to get operator precedence right. That said, the ?Syntax help
topic hasn't been updated, so I'm not sure where it fits in.
There are some choices that take a little getting used to:
> mtcars |> head
Error: The pipe operator requires a function call or an anonymous
function expression as RHS
(I need to say mtcars |> head() instead.) This sometimes leads to error
messages that are somewhat confusing:
> mtcars |> magrittr::debug_pipe |> head
Error: function '::' not supported in RHS call of a pipe
but
mtcars |> magrittr::debug_pipe() |> head()
works.
Overall, I think this is a great addition, though it's going to be
disruptive for a while.
Duncan Murdoch
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