bug in functions of form "mcpar<-"

[Martyn Plummer]

Peter Dalgaard BSA wrote:

> Hmm. We had some pretty antisocial consequences from *not* using the
> value= form with John Chambers' [<-.data.frame code, which assumes
> that it is used that way in order to see whether i,j, or both are
> absent.
> 
> So Splus is using value= on indexing operations only?

Looks like it.  As I said, my other example works in S-PLUS, but try
doing
the same thing with an assignment on an index and you get an error:
(This examples is obviously silly in order to distinguish it from the
default
indexing function).

S> "[<-.foo" <-
function(x,i,value){y<-unclass(x);y[i]<-value+1;class(y)<-"foo";y}
S> x <- 1:10
S> class(x) <- "foo"
S> x[1]<-100
S> x
 [1] 101   2   3   4   5   6   7   8   9  10
attr(, "class"):
[1] "foo"
S> "[<-.foo" <-
function(x,i,bar){y<-unclass(x);y[i]<-bar+1;class(y)<-"foo";y}
S> x[1]<-200
Error in call to [<-.foo(): Argument value= not matched
Dumped

Martyn
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