Browsing after an Error

Description

This function allows the user to browse directly on any of the currently active function calls, and is suitable as an error option. The expression options(error=recover) will make this the error option.

Usage

recover()

Details

When called, recover prints the list of current calls, and prompts the user to select one of them. The standard R browser is then invoked from the corresponding environment; the user can type ordinary S language expressions to be evaluated in that environment.

When finished browsing in this call, type c to return to recover from the browser. Type another frame number to browse some more, or type 0 to exit recover.

The use of recover largely supersedes dump.frames as an error option, unless you really want to wait to look at the error. If recover is called in non-interactive mode, it behaves like dump.frames. For computations involving large amounts of data, recover has the advantage that it does not need to copy out all the environments in order to browse in them. If you do decide to quit interactive debugging, call dump.frames directly while browsing in any frame (see the examples).

WARNING: The special Q command to go directly from the browser to the prompt level of the evaluator currently interacts with recover to effectively turn off the error option for the next error (on subsequent errors, recover will be called normally).

Value

Nothing useful is returned. However, you can invoke recover directly from a function, rather than through the error option shown in the examples. In this case, execution continues after you type 0 to exit recover.

Compatibility Note

The R recover function can be used in the same way as the S-Plus function of the same name; therefore, the error option shown is a compatible way to specify the error action. However, the actual functions are essentially unrelated and interact quite differently with the user. The navigating commands up and down do not exist in the R version; instead, exit the browser and select another frame.

References

John M. Chambers (1998). Programming with Data; Springer.
See the compatibility note above, however.

See Also

browser for details about the interactive computations; options for setting the error option; dump.frames to save the current environments for later debugging.

Examples

## Not run: 

options(error = recover) # setting the error option

### Example of interaction

> myFit <- lm(y ~ x, data = xy, weights = w)
Error in lm.wfit(x, y, w, offset = offset, ...) :
        missing or negative weights not allowed

Enter a frame number, or 0 to exit
1:lm(y ~ x, data = xy, weights = w)
2:lm.wfit(x, y, w, offset = offset, ...)
Selection: 2
Called from: eval(expr, envir, enclos)
Browse[1]> objects() # all the objects in this frame
[1] "method" "n"      "ny"     "offset" "tol"    "w"
[7] "x"      "y"
Browse[1]> w
[1] -0.5013844  1.3112515  0.2939348 -0.8983705 -0.1538642
[6] -0.9772989  0.7888790 -0.1919154 -0.3026882
Browse[1]> dump.frames() # save for offline debugging
Browse[1]> c # exit the browser

Enter a frame number, or 0 to exit
1:lm(y ~ x, data = xy, weights = w)
2:lm.wfit(x, y, w, offset = offset, ...)
Selection: 0 # exit recover
>

## End(Not run)