On 29 Oct 2004, Peter Dalgaard wrote:
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
That's not the issue: VectorAssign has identical code for the vector list
and expression cases. The issue is in SubassignTypeFix which says
case 2010: /* expression <- logical */
/* Note : No coercion is needed here. */
/* We just insert the RHS into the LHS. */
/* FIXME: is this true or should it be just like the "vector" case? */
and at level=1 the FIXME is correct.
Brian
Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595