Support for user defined unary functions
Your example
x = 5
exp = parse(text="f(uq(x)) + y +z") # expression: f(uq(x)) +y + z
do_unquote(expr)
# -> the language object f(5) + y + z
could be done with the following wrapper for bquote
my_do_unquote <- function(language, envir = parent.frame()) {
if (is.expression(language)) {
# bquote does not go into expressions, only calls
as.expression(lapply(language, my_do_unquote))
} else {
do.call(bquote, list(language, where=envir))
}
}
as in
> x <- 5
> exp <- parse(text="f(.(x)) + y +z") # dot is uq for bquote
> exp
expression(f(.(x)) + y +z)
> my_do_unquote(exp)
expression(f(5) + y + z)
Or do uq() and do_unquote() do more than that? E.g., would
uq() carry information about environments?
[I think expressions should map to expressions and calls to calls.
Otherwise what would we do with multicall expressions?]
We probably need to come up with a better name than 'non-standard
evaluation' since there are lots of non-standard ways of doing things.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Fri, Mar 17, 2017 at 12:14 PM, Gabriel Becker <gmbecker at ucdavis.edu> wrote:
William, Unbeknownst to me when I sent this, Jonathon Carrol started a specific thread about unquoting and a proposal for supporting it at the language level, which I think is a better place to discuss unquoting specifically. That said, the basics as I understand them in the context of non-standard evaluation, unquoting (or perhaps interpolation) is essentially substituting part of an unevaluated expression with its evaluated value inlined. The unquote operator, then, is the way of marking which parts of the expression should be substituted in that way (i.e. interpolated). i.e. if uq() is the unquote "operator" and do_unquote interpolates, then if we have x = 5 exp = parse(text="f(uq(x)) + y +z") # expression: f(uq(x)) +y + z Then do_unquote would give you the expression f(5) + y + z In terms of what it does that the tilde does not, it would give you the ability to partially evaluate the captured formula/expression, without fully doing so. See the roxygen comments in Hadley and Lionel's rlang package here: https://github.com/hadley/rlang/blob/master/R/tidy-unquote.R The desired precedence of such a unary operator is not clear to me. The way rlang implements the !! now, it is quite low, so in the examples you see there the ~list(!! x + x) is transformed to ~list(10), not ~list(5+x) as I would have expected. I'm confused by this given what I understand the purpose to be, but that probably just means I'm not the right person to ask. Hope that helps. Best, ~G On Fri, Mar 17, 2017 at 8:55 AM, William Dunlap <wdunlap at tibco.com> wrote:
After off list discussions with Jonathan Carrol and with Michael Lawrence I think it's doable, unambiguous, and even imo pretty intuitive for an "unquote" operator.
For those of us who are not CS/Lisp mavens, what is an "unquote" operator? Can you expression quoting and unquoting in R syntax and show a few examples where is is useful, intuitive, and fits in to R's functional design? In particular, what does it give us that the current tilde function does not? Bill Dunlap TIBCO Software wdunlap tibco.com On Fri, Mar 17, 2017 at 6:46 AM, Gabriel Becker <gmbecker at ucdavis.edu> wrote:
Jim, One more note about precedence. It prevents a solution like the one you proposed from solving all of the problems you cited. By my reckoning, a "What comes next is for NSE" unary operator needs an extremely low precedence, because it needs to greedily grab "everything" (or a large amount) that comes after it. Normal-style unary operators, on the other hand, explicitly don't want that. From what I can see, your patch provides support for the latter but not the former. That said I think there are two issues here. One is can users define unary operators. FWIW my opinion on that is roughly neutral to slightly positive. The other issue is can we have quasi quotation of the type that Hadley and Lionel need in the language. This could be solved without allowing user-defined unary specials, and we would probably want it to be, as I doubt ~ %!%x + %!%y + z is particularly aesthetically appealing to most (it isn't to me). I'd propose coopting unary @ for that myself. After off list discussions with Jonathan Carrol and with Michael Lawrence I think it's doable, unambiguous, and even imo pretty intuitive for an "unquote" operator. Best, ~G On Fri, Mar 17, 2017 at 5:10 AM, Jim Hester <james.f.hester at gmail.com> wrote:
I agree there is no reason they _need_ to be the same precedence, but
I think SPECIALS are already have the proper precedence for both unary
and binary calls. Namely higher than all the binary operators (except
for `:`), but lower than the other unary operators. Even if we gave
unary specials their own precedence I think it would end up in the
same place.
`%l%` <- function(x) tail(x, n = 1)
%l% 1:5
#> [1] 5
%l% -5:-10
#> [1] -10
On Thu, Mar 16, 2017 at 6:57 PM, William Dunlap <wdunlap at tibco.com>
wrote:
I am biased against introducing new syntax, but if one is experimenting with it one should make sure the precedence feels right. I think the unary and binary minus-sign operators have different precedences so I see no a priori reason to make the unary and binary %xxx% operators to be the same. Bill Dunlap TIBCO Software wdunlap tibco.com On Thu, Mar 16, 2017 at 3:18 PM, Michael Lawrence <lawrence.michael at gene.com> wrote:
I guess this would establish a separate "namespace" of symbolic prefix operators, %*% being an example in the infix case. So you could have stuff like %?%, but for non-symbolic (spelled out stuff like %foo%), it's hard to see the advantage vs. foo(x). Those examples you mention should probably be addressed (eventually) in the core language, and it looks like people are already able to experiment, so I'm not sure there's a significant impetus for this change. Michael On Thu, Mar 16, 2017 at 10:51 AM, Jim Hester <james.f.hester at gmail.com> wrote:
I used the `function(x)` form to explicitly show the function was being called with only one argument, clearly performance implications are not relevant for these examples. I think of this mainly as a gap in the tooling we provide users and package authors. R has native prefix `+1`, functional `f(1)` and infix `1 + 1` operators, but we only provide a mechanism to create user defined functional and infix operators. One could also argue that the user defined infix operators are also ugly and could be replaced by `f(a, b)` calls as well; beauty is in the eye of the beholder. The unquote example [1] shows one example where this gap in tooling caused authors to co-opt existing unary exclamation operator, this same gap is part of the reason the formula [2] and question mark [3] operators have been used elsewhere in non standard contexts. If the language provided package authors with a native way to create unary operators like it already does for the other operator types these machinations would be unnecessary. [1]: https://github.com/hadley/rlang/blob/master/R/tidy-unquote.R#L17 [2]: https://cran.r-project.org/package=ensurer [3]: https://cran.r-project.org/package=types On Thu, Mar 16, 2017 at 1:04 PM, Gabriel Becker <gmbecker at ucdavis.edu> wrote:
Martin, Jim can speak directly to his motivations; I don't claim to be able to do so. That said, I suspect this is related to a conversation on twitter
about
wanting an infix "unquote" operator in the context of the non-standard evaluation framework Hadley Wickham and Lionel Henry (and possibly
others)
are working on. They're currently using !!! and !! for things related to this, but this effectively requires non-standard parsing, as ~!!x is interpreted as ~(`!!`(x)) rather than ~(!(!(x)) as the R parser understands it. Others
and
I pointed out this was less than desirable, but if something like it was going to happen it would hopefully happen in the language specification, rather than in a package (and also hopefully not using !! specifically). Like you, I actually tend to prefer the functional form myself in most cases. There are functional forms that would work for the above case
(e.g.,
something like the .() that DBI uses), but that's probably off topic
here,
and not a decision I'm directly related to anyway. Best, ~G On Thu, Mar 16, 2017 at 9:51 AM, Martin Maechler <maechler at stat.math.ethz.ch> wrote:
Jim Hester <james.f.hester at gmail.com>
on Thu, 16 Mar 2017 12:31:56 -0400 writes:
> Gabe,
> The unary functions have the same precedence as normal
SPECIALS
> (although the new unary forms take precedence over binary
SPECIALS).
> So they are lower precedence than unary + and -. Yes, both
of your
> examples are valid with this patch, here are the results
and
quoted
> forms to see the precedence.
> `%chr%` <- function(x) as.character(x)
[more efficient would be `%chr%` <- as.character]
> `%identical%` <- function(x, y) identical(x, y)
> quote("100" %identical% %chr% 100)
> #> "100" %identical% (`%chr%`(100))
> "100" %identical% %chr% 100
> #> [1] TRUE
> `%num%` <- as.numeric
> quote(1 + - %num% "5")
> #> 1 + -(`%num%`("5"))
> 1 + - %num% "5"
> #> [1] -4
> Jim
I'm sorry to be a bit of a spoiler to "coolness", but
you may know that I like to applaud Norm Matloff for his book
title "The Art of R Programming",
because for me good code should also be beautiful to some
extent.
I really very much prefer
f(x)
to %f% x
and hence I really really really cannot see why anybody would
prefer
the ugliness of
1 + - %num% "5"
to
1 + -num("5")
(after setting num <- as.numeric )
Martin
> On Thu, Mar 16, 2017 at 12:01 PM, Gabriel Becker
<gmbecker at ucdavis.edu> wrote:
>> Jim,
>>
>> This seems cool. Thanks for proposing it. To be concrete,
he user-defined
>> unary operations would be of the same precedence (or just
slightly
below?)
>> built-in unary ones? So
>>
>> "100" %identical% %chr% 100
>>
>> would work and return TRUE under your patch?
>>
>> And with %num% <- as.numeric, then
>>
>> 1 + - %num% "5"
>>
>> would also be legal (though quite ugly imo) and work?
>>
>> Best,
>> ~G
>>
>> On Thu, Mar 16, 2017 at 7:24 AM, Jim Hester
<james.f.hester at gmail.com>
>> wrote:
>>>
>>> R has long supported user defined binary (infix)
functions, defined
>>> with `%fun%`. A one line change [1] to R's grammar
allows users
to
>>> define unary (prefix) functions in the same manner.
>>>
>>> `%chr%` <- function(x) as.character(x)
>>> `%identical%` <- function(x, y) identical(x, y)
>>>
>>> %chr% 100
>>> #> [1] "100"
>>>
>>> %chr% 100 %identical% "100"
>>> #> [1] TRUE
>>>
>>> This seems a natural extension of the existing
functionality and
>>> requires only a minor change to the grammar. If this
change
seems
>>> acceptable I am happy to provide a complete patch with
suitable tests
>>> and documentation.
>>>
>>> [1]:
>>> Index: src/main/gram.y
>>>
===================================================================
>>> --- src/main/gram.y (revision 72358)
>>> +++ src/main/gram.y (working copy)
>>> @@ -357,6 +357,7 @@
>>> | '+' expr %prec UMINUS { $$ =
xxunary($1,$2);
>>> setId( $$, @$); }
>>> | '!' expr %prec UNOT { $$ =
xxunary($1,$2);
>>> setId( $$, @$); }
>>> | '~' expr %prec TILDE { $$ =
xxunary($1,$2);
>>> setId( $$, @$); }
>>> + | SPECIAL expr { $$ =
xxunary($1,$2);
>>> setId( $$, @$); }
>>> | '?' expr { $$ =
xxunary($1,$2);
>>> setId( $$, @$); }
>>>
>>> | expr ':' expr { $$ =
>>> xxbinary($2,$1,$3); setId( $$, @$); }
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>>
>>
>> --
>> Gabriel Becker, PhD
>> Associate Scientist (Bioinformatics)
>> Genentech Research
> ______________________________________________
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> https://stat.ethz.ch/mailman/listinfo/r-devel
-- Gabriel Becker, PhD Associate Scientist (Bioinformatics) Genentech Research
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-- Gabriel Becker, PhD Associate Scientist (Bioinformatics) Genentech Research