From lukas.stadler at oracle.com  Mon Jan  4 17:09:31 2016
From: lukas.stadler at oracle.com (Lukas Stadler)
Date: Mon, 4 Jan 2016 17:09:31 +0100
Subject: [Rd] deparse with parentheses for SUBSET
Message-ID: <EFE63DD3-7E5D-4C56-A7C1-32124558B863@oracle.com>

Hi,

maybe there?s a reason for it, but the discrepancy between the handling of `[` and `$` in deparsing seems odd to me:
> substitute(a[1], list(a = quote(x * y)))
x * y[1]
> substitute(a$b, list(a = quote(x * y)))
(x * y)$b

The former is still executed in the right order (`*` first, then `[`), which is not what you?d expect looking at the deparse result.
Some code that shows the execution order:
x <- 1; y <- 1; class(y) <- "foo"; `*.foo` <- function(...) -1; expr <- substitute(a[1], list(a=quote(x * y))); list(expr=expr, eval=eval(expr), "x * y[1]"=x * y[1], "(x * y)[1]"=(x * y)[1])

The following simple fix solves the problem for me:

diff -u -r A/src/main/deparse.c B/src/main/deparse.c
--- R-devel 2/src/main/deparse.c	2015-08-09 18:09:04.000000000 +0200
+++ R-devel/src/main/deparse.c	2016-01-04 16:15:09.000000000 +0100
@@ -971,7 +971,11 @@
 		    print2buff(")", d);
 		    break;
 		case PP_SUBSET:
+		    if ((parens = needsparens(fop, CAR(s), 1)))
+			print2buff("(", d);
 		    deparse2buff(CAR(s), d);
+		    if (parens)
+			print2buff(")", d);
 		    if (PRIMVAL(SYMVALUE(op)) == 1)
 			print2buff("[", d);
 		    else

With this applied, the output is more consistent:
> substitute(a[1], list(a = quote(x * y)))
(x * y)[1]
> substitute(a$b, list(a = quote(x * y)))
(x * y)$b

Best Regards,
 Lukas Stadler


[Rd] deparse with parentheses for SUBSET
Lukas Stadler