[Rd] Support for user defined unary functions
William Dunlap
wdunlap at tibco.com
Fri Mar 17 20:53:09 CET 2017
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
>> >> >>> >>
>> >> >>> >> > ______________________________________________
>> >> >>> >> > 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
>
>
>
>
> --
> Gabriel Becker, PhD
> Associate Scientist (Bioinformatics)
> Genentech Research
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