R devel - Oct 2004 - (inappropriate) manipulation of expression objects causes segfault (PR#7326)

> version
         _
platform i686-pc-linux-gnu
arch     i686
os       linux-gnu
system   i686, linux-gnu
status   Under development (unstable)
major    2
minor    1.0
year     2004
month    10
day      25
language R
>
> foo <- expression(alpha, beta, gamma)
> foo[2]
expression(beta)
> foo[2] <- NA
> foo ## or str(foo)
Segmentation fault

(Same behaviour in R 1.9.1)

'foo[[2]] <- NA' works fine, though.

Deepayan

deepayan@stat.wisc.edu writes:
> > foo <- expression(alpha, beta, gamma)
> > foo[2]
> expression(beta)
> > foo[2] <- NA
> > foo ## or str(foo)
> Segmentation fault
> 
> (Same behaviour in R 1.9.1)
> 
> 'foo[[2]] <- NA' works fine, though.
Right. The NA is not important; foo[2] <- 1 crashes R just as
effectively. We should likely either give an error or demote [ to [[.
The latter is what happens with lists, and expressions are basically
just list of call objects (or names or constants). To wit:
> x <- list(1,2,3)
> x[2] <- 1
> x
[[1]]
[1] 1

[[2]]
[1] 1

[[3]]
[1] 3

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907