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 { $$ =
xxbinary($2,$1,$3); setId( $$, @$); }
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