From wdunlap at tibco.com  Thu Mar 16 23:57:38 2017
From: wdunlap at tibco.com (William Dunlap)
Date: Thu, 16 Mar 2017 15:57:38 -0700
Subject: [Rd] Support for user defined unary functions
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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
>>
>
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[Rd] Support for user defined unary functions
William Dunlap