debugger
Post-Mortem Debugging
Functions to dump the evaluation environments (frames) and to examine dumped frames.
Usage
dump.frames(dumpto = "last.dump", to.file = FALSE)
debugger(dump = last.dump)Arguments
- dumpto
- a character string. The name of the object or file to dump to.
- to.file
- logical. Should the dump be to an Robject or to a file?
- dump
- An Rdump object created by
dump.frames.
Details
To use post-mortem debugging, set the option error to be a call
to dump.frames. By default this dumps to an Robject
last.dump in the workspace, but it can be set to dump to a
file (a dump of the object produced by a call to save).
The dumped object contain the call stack, the active environments and
the last error message as returned by geterrmessage.
When dumping to file, dumpto gives the name of the dumped
object and the file name has
A dump object of class "dump.frames" can be examined by calling
debugger. This will give the error message and a list of
environments from which to select repeatedly. When an environment is
selected, it is copied and the browser called from
within the copy. Note that not all the information in the original
frame will be available, e.g.... argument.
If dump.frames is installed as the error handler, execution
will continue even in non-interactive sessions. See the examples for
how to dump and then quit.
Value
- Invisible
NULL.
Note
Functions such as sys.parent and
environment applied to closures will not work correctly
inside debugger.
If the error occurred when computing the default value of a formal
argument the debugger will report
Of course post-mortem debugging will not work if Ris too damaged to produce and save the dump, for example if it has run out of workspace.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
browser for the actions available at the Browse
prompt.
options for setting error options;
recover is an interactive debugger working similarly to
debugger but directly after the error occurs.
Examples
library(utils)
options(error = quote(dump.frames("testdump", TRUE)))
f <- function() {
g <- function() stop("test dump.frames")
g()
}
f() # will generate a dump on file "testdump.rda"
options(error = NULL)
## possibly in another R session
load("testdump.rda")
debugger(testdump)
Available environments had calls:
1: f()
2: g()
3: stop("test dump.frames")
Enter an environment number, or 0 to exit
Selection: 1
Browsing in the environment with call:
f()
Called from: debugger.look(ind)
Browse[1]> ls()
[1] "g"
Browse[1]> g
function() stop("test dump.frames")
<environment: 759818>
Browse[1]>
Available environments had calls:
1: f()
2: g()
3: stop("test dump.frames")
Enter an environment number, or 0 to exit
Selection: 0
## A possible setting for non-interactive sessions
options(error = quote({dump.frames(to.file = TRUE); q(status = 1)}))