R devel - Nov 2000 - substitute(x$y)) corrupts 'y' component (PR#731)

viz.

> (function(x,y=a) substitute(x$y))(x)
x$a
> (function(x,y=a) substitute(x$y))(list(y=1:3))
list(y = 1:3)$a
> (function(x,y) eval(substitute(substitute(y))))(x=list(y=1:3),y=x$y)
list(y = 1:3)$x$y


The behavior I expect and want is like that in Splus 3.4:
> (function(x,y=a) substitute(x$y))(x)
x$y
> (function(x,y=a) substitute(x$y))(list(y=1:3))
list(y = 1:3)$y
> (function(x,y) eval(substitute(substitute(y))))(x=list(y=1:3),y=x$y)
list(y = 1:3)$y

Is there a workaround to achieve this behavior under fairly general
circumstances, i.e. when one does not know whether to expect an object
with a component, but encounters one?

Chuck Berry
--please do not edit the information below--

Version:
 platform = sparc-sun-solaris2.7
 arch = sparc
 os = solaris2.7
 system = sparc, solaris2.7
 status = 
 major = 1
 minor = 1.0
 year = 2000
 month = June
 day = 15
 language = R

Search Path:
 .GlobalEnv, package:bqtl, Autoloads, package:base
> 
-- 
Charles C. Berry                        (858) 534-2098 
                                         Dept of Family/Preventive
Medicine
E mailto:cberry@tajo.ucsd.edu	         UC San Diego
http://hacuna.ucsd.edu/members/ccb.html  La Jolla, San Diego 92093-0645

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To:
r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

On Wed, 8 Nov 2000 cberry@tajo.ucsd.edu wrote:
> viz.
> 
> 
> > (function(x,y=a) substitute(x$y))(x)
> x$a
> > (function(x,y=a) substitute(x$y))(list(y=1:3))
> list(y = 1:3)$a
> > (function(x,y) eval(substitute(substitute(y))))(x=list(y=1:3),y=x$y)
> list(y = 1:3)$x$y
> 
> 
> The behavior I expect and want is like that in Splus 3.4:
> 
> > (function(x,y=a) substitute(x$y))(x)
> x$y
> > (function(x,y=a) substitute(x$y))(list(y=1:3))
> list(y = 1:3)$y
> > (function(x,y) eval(substitute(substitute(y))))(x=list(y=1:3),y=x$y)
> list(y = 1:3)$y

I don't think this is a bug - substitute is performing as intended and as
documented -- but it is an incompatibility.  There are two issues here,
one easy and one difficult.

In your first two examples the problem is that you want to substitute only
for x (though in the second example I don't see why you expect this to
happen).  If you want to substitute only for x you can do
	substitute(x$y,list(x=x))


In the third example you want to perform substitution on the value of a
variable.  This is a useful thing to want to do, and I don't know how to
do it.

eg
     z<-quote(x$y)
     x<-list(y=1:3)
and you want to produce
     list(y=1:3)$y

Suggestions?

	-thomas

Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To:
r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._