>>>>> "PD" == Peter Dalgaard <[EMAIL PROTECTED]>
>>>>> on Fri, 16 Mar 2007 08:09:00 +0100 writes:
PD> Seth Falcon wrote:
>> [EMAIL PROTECTED] writes:
>>
>>> Investigating this new implementation I come across an issue in
>>> conjuntion with using S4 classes and methods. try(expr) does not return
an
>>> object with attribute 'try-error' in case of method dispatch failure
>>> in the wrapped expression which to me seems not
>>> quite correct.
>>>
>>
>> We've seen some similar issues but had not had time to track them
>> down.
>>
>>
>>> Examples to reproduce the observation:
>>>
>>
>> It isn't S4 specific. The issue seems more about anonymous
>> calls/functions.
>>
>> ll = list()
>> ll[[1]] = function(x) stop("died")
>>
>> v = try(do.call(ll[[1]], list(1)), silent=TRUE)
>> Error in as.list(call)[[1]] == "doTryCatch" :
>> comparison (1) is possible only for atomic and list types
>> > v
>> Error: object "v" not found
>>
>> I don't fully understand why the call is being computed, but the
>> following seems to get things going.
>>
>> + seth
>>
>> --- a/src/library/base/R/New-Internal.R
>> +++ b/src/library/base/R/New-Internal.R
>> @@ -7,7 +7,8 @@ try <- function(expr, silent = FALSE) {
>> ## Patch up the call to produce nicer result for testing as
>> ## try(stop(...)). This will need adjusting if the
>> ## implementation of tryCatch changes.
>> - if (as.list(call)[[1]] == "doTryCatch")
>> + callFun <- as.list(call)[[1]]
>> + if (is.name(callFun) && callFun == "doTryCatch")
>> call <- sys.call(-4)
>> dcall <- deparse(call)[1]
>> prefix <- paste("Error in", dcall, ": ")
>>
>>
PD> Good catch, Seth.
yes, indeed!
PD> The code still looks a bit clunky though, and I wonder
PD> if this wouldn't be nicer:
PD> if (identical(call[[1]], quote(doTryCatch))) call <- sys.call(-4)
PD> I.e., the thing that is clearly wrong is the use of "==" on something
PD> that is not necessarily a simple name, but the use of as.list seems
PD> unnecessary and comparisons between strings and names is a bit awkward
too.
Indeed, I had similar thoughts when reading the part of code
Seth was patching
{ but would have used the old-fashioned as.name("doTryCatch")
instead of the modern quote(doTryCatch)
for the only reason that I'm probably slightly ``older fashioned''
than Peter ;-)
}
Martin
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