[Rd] Support for user defined unary functions
William Dunlap
wdunlap at tibco.com
Fri Mar 17 16:55:03 CET 2017
>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
>> >>> >>
>> >>> >> > ______________________________________________
>> >>> >> > R-devel at r-project.org mailing list
>> >>> >> > https://stat.ethz.ch/mailman/listinfo/r-devel
>> >>> >
>> >>> >
>> >>> >
>> >>> >
>> >>> > --
>> >>> > Gabriel Becker, PhD
>> >>> > Associate Scientist (Bioinformatics)
>> >>> > Genentech Research
>> >>>
>> >>> ______________________________________________
>> >>> R-devel at r-project.org mailing list
>> >>> https://stat.ethz.ch/mailman/listinfo/r-devel
>> >>>
>> >>
>> >> [[alternative HTML version deleted]]
>> >>
>> >> ______________________________________________
>> >> R-devel at r-project.org mailing list
>> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>> ______________________________________________
>> 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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