[Rd] Support for user defined unary functions

[Gabriel Becker]

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

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