This works the same way as `?` is defined in R code, and `-`, `+`
(defined in C) do now, you define one function that handles calls with
both unary and binary arguments.
quote(a %f% %f% b)
#> a %f% (`%f%`(b))
`%f%` <- function(a, b) if (missing(b)) { force(a); cat("unary\n")
} else { force(a);force(b);cat("binary\n") }
a <- 1
b <- 2
a %f% %f% b
#> unary
#> binary
This also brings up the point about what happens to existing user
defined functions such as `%in%` when they are used as unary functions
(likely by mistake). Happily this provides a useful error when run
assuming no default value of the second argument.
%in% a
#> Error in match(x, table, nomatch = 0L) :
#> argument "table" is missing, with no default
On Thu, Mar 16, 2017 at 7:13 PM, Duncan Murdoch
<murdoch.dun...@gmail.com> wrote:
> I don't have a positive or negative opinion on this yet, but I do have a
> question. If I define both unary and binary operators with the same name
> (in different frames, presumably), what would happen?
>
> Is "a %chr% b" a syntax error if unary %chr% is found first? If both might
> be found, does "a %chr% %chr% b" mean "%chr%(a, %chr% b)", or is it a syntax
> error (like typing "a %chr%(%chr%(b))" would be)?
>
> Duncan Murdoch
>
>
>
>
>
> On 16/03/2017 10:24 AM, Jim Hester 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@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
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