>>>>> "PD" == p dalgaard
<p.dalgaard@biostat.ku.dk> writes:
PD> [sys.function fails sometimes (sorry, our mail system
PD> decide to throw away the original mail)]
PD> Yes, I bumped into something similar recently. The
PD> problem is that we only actually store the call in the
PD> context structure, not the function, so sys.function has
PD> to grab the call, take the 1st element, and reevaluate
PD> it in the parent frame. It is quite easy to think up
PD> examples where a second evaluation does not give the
PD> same value as the first.
PD> Your particular case is of a slightly different natur
PD> and should be easily fixable by replacing findVar in
PD> R_sysfunction by findVar1 and looking specifically for
PD> objects of mode "function", but the basic problem
PD> persists. I don't think I want to risk fixing this (and
PD> maybe unfixing something else) for 1.2.3 tomorrow
PD> though.
and Peter *did* implement the ``stop gap'' fix above for 1.5.0,
but the proper fix (for the more general problem) is still to be
done.
Martin
JonR> From: J.C.Rougier@durham.ac.uk
JonR> Date: Wed, 25 Apr 2001 13:23:09 +0200 (MET DST)
...
JonR> This one may not strictly be a bug, and it was
JonR> certainly my fault, but it took me a while to track it
JonR> down and it is rather strange:
(it *is* bug)
funOne <- function(x) { funTwo <- 1:10 ; funTwo(x) }
funTwo <- function(v) 2*v
funOne(5) # answer is 10 as expected
# now a different definition for funTwo with a match.arg
funTwo <- function(v, foo=c("small", "large")) {
foo <- match.arg(foo); print(foo); 2*v }
funOne(5) # answer is 10, but foo is NULL
JonR> What happens is that in funOne I mask funTwo with a
JonR> vector, but that doesn't matter as the call to funTwo
JonR> specifies mode="function" (or something similar). But
JonR> what happens when funTwo includes a match.arg? In
JonR> this case match.arg fails, and the reason it fails is
JonR> that sys.function(sys.parent()) in match.arg evaluates
JonR> to 1:10. If there is a bug here it is the failure of
JonR> sys.function to grab a function, with the result that
JonR> formal.args in match.fun is NULL.
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