> On 7 Dec 2020, at 17:35 , Duncan Murdoch <murdoch.duncan at
gmail.com> wrote:
>
> On 07/12/2020 11:18 a.m., peter dalgaard wrote:
>> Hmm,
>> I feel a bit bad coming late to this, but I think I am beginning to
side with those who want "... |> head" to work. And yes, that has
to happen at the expense of |> head().
>
> Just curious, how would you express head(df, 10)? Currently it is
>
> df |> head(10)
>
> Would I have to write it as
>
> df |> function(d) head(d, 10)
It could be
df |> ~ head(_, 10)
which in a sense is "yes" to your question.
>
>> As I think it was Gabor points out, the current structure goes down a
nonstandard evaluation route, which may be difficult to explain and departs from
usual operator evaluation paradigms by being an odd mix of syntax and semantics.
R lets you do these sorts of thing, witness ggplot and tidyverse, but the
transparency of the language tends to suffer.
>
> I wouldn't call it non-standard evaluation. There is no function
corresponding to |>, so there's no evaluation at all. It is more like
the way "x -> y" is parsed as "y <- x", or "if
(x) y" is transformed to `if`(x, y).
That's a point, but maybe also my point. Currently, the parser is inserting
the LHS as the 1st argument of the RHS, right? Things might be simpler if it was
more like a simple binop.
-pd
> Duncan Murdoch
>
>> It would be neater if it was simply so that the class/type of the
object on the right hand side decided what should happen. So we could have a
rule that we could have an object, an expression, and possibly an unevaluated
call on the RHS. Or maybe a formula, I.e., we could hav
>> ... |> head
>> but not
>> ... |> head()
>> because head() does not evaluate to anything useful. Instead, we could
have some of these
>> ... |> quote(head())
>> ... |> expression(head())
>> ... |> ~ head()
>> ... |> \(_) head(_)
>> possibly also using a placeholder mechanism for the three first ones. I
kind of like the idea that the ~ could be equivalent to \(_).
>> (And yes, I am kicking myself a bit for not using ~ in the NSE
arguments in subset() and transform())
>> -pd
>>> On 7 Dec 2020, at 16:20 , Deepayan Sarkar <deepayan.sarkar at
gmail.com> wrote:
>>>
>>> On Mon, Dec 7, 2020 at 6:53 PM Gabor Grothendieck
>>> <ggrothendieck at gmail.com> wrote:
>>>>
>>>> On Mon, Dec 7, 2020 at 5:41 AM Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
>>>>> I agree it's all about call expressions, but they
aren't all being
>>>>> treated equally:
>>>>>
>>>>> x |> f(...)
>>>>>
>>>>> expands to f(x, ...), while
>>>>>
>>>>> x |> `function`(...)
>>>>>
>>>>> expands to `function`(...)(x). This is an exception to the
rule for
>>>>> other calls, but I think it's a justified one.
>>>>
>>>> This admitted inconsistency is justified by what? No argument
has been
>>>> presented. The justification seems to be implicitly driven by
implementation
>>>> concerns at the expense of usability and language consistency.
>>>
>>> Sorry if I have missed something, but is your consistency argument
>>> basically that if
>>>
>>> foo <- function(x) x + 1
>>>
>>> then
>>>
>>> x |> foo
>>> x |> function(x) x + 1
>>>
>>> should both work the same? Suppose it did. Would you then be OK if
>>>
>>> x |> foo()
>>>
>>> no longer worked as it does now, and produced foo()(x) instead of
foo(x)?
>>>
>>> If you are not OK with that and want to retain the current
behaviour,
>>> what would you want to happen with the following?
>>>
>>> bar <- function(x) function(n) rnorm(n, mean = x)
>>>
>>> 10 |> bar(runif(1))() # works 'as expected' ~
bar(runif(1))(10)
>>> 10 |> bar(runif(1)) # currently bar(10, runif(1))
>>>
>>> both of which you probably want. But then
>>>
>>> baz <- bar(runif(1))
>>> 10 |> baz
>>>
>>> (not currently allowed) will not be the same as what you would want
from
>>>
>>> 10 |> bar(runif(1))
>>>
>>> which leads to a different kind of inconsistency, doesn't it?
>>>
>>> -Deepayan
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk Priv: PDalgd at gmail.com