R 2.5.0 devel try issue in conjuntion with S4 method dispatch

ml-it-r-devel at epigenomics.com 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, ": ")

Seth Falcon | Computational Biology | Fred Hutchinson Cancer Research Center
http://bioconductor.org