Hi Emil,
First, thanks for the response. As you mentioned, a lot of times tryCatch
does the work, as you can return a value. However, sometimes it is useful
to assign several variables when an error occurs. You could do it with <<-,
but I prefer to reduce it's usage unless completely necessary.
I guess that the attachment was missed in the moderation. Here it is the
function:
tryExcept <- function (expr,
except = {})
{
doTryExcept <- function(expr, parentenv) {
.Internal(.addCondHands("error", list(NULL), parentenv,
environment(), FALSE))
expr
}
parentenv <- parent.frame()
doTryExcept(return(expr), parentenv)
invisible(except)
}
As you can see, the tryExcept function uses a simplified version of the
tryCatch architecture, but it allows you to pass by a second expression
that is evaluated in case an error occurs during the evaluation of the
first expression. It could even work as an infix operator:
`%except%` <- tryExcept
# dummy example
{foo <- "foo"} %except% {foo <- "foo bar"}
print(foo) # "foo"
{ foo <- "foo"
stop()
} %except% {
foo <- "foo bar"
}
print(foo) # "foo bar"
It's main downside is that you are not able to handle the error occured,
although there is the possibility to add a 'silent' parameter such as in
'try' in order to print the error if desired. All in all, this would be a
function for simple error handling, but I think it would be practical, and
you can always move to tryCatch if you need a more complex error handling.
I will be looking forward to hearing your insights.
Best,
Ernest Benedito
Missatge de Emil Bode <emil.bode at dans.knaw.nl> del dia dv., 23 de nov.
2018
a les 13:17:
Hi Ernest,
To start: I don't see an attachment, I think they're not (always) allowed
on this mailing-list. If you want to send something, text is your safest
bet.
But regarding the issue of tryCatch: I think you're not fully using what
it already can do. In almost all circumstances I've encountered the
following works fine:
res <- tryCatch(expr, error = function(cond) {
# a bunch of code
# Some value to be stored in res
})
The only difference is that now "#abunchofcode" is run from inside a
function, which means you're working in a different environment, and if
want to assign values to other variables you need to use <<- or assign.
For a modified function, I think it would be nice if there's a way to
supply an expression instead of a function, so that evaluation (and
assignment!) takes place in the same environment as the main code in the
tryCatch (in expr). Is that what you made?
And with the current tryCatch, you could use something like this:
res <- tryCatch(expr, error=function(e) evalq({
# a bunch of code
# Some value for res
}, envir=parent.frame(4))) # The 4 is because some internal functions are
involved, parent.frame(4) is the same environment as used by expr
Although this is cumbersome, and it gets even more cumbersome if you want
to access the error-object in #abunchofcode, or use #abunchofcode to
to a higher level, so I get it you're looking for a more elegant
Best regards,
Emil Bode
?On 23/11/2018, 08:49, "R-devel on behalf of Ernest Benedito" <
r-devel-bounces at r-project.org on behalf of ebeneditos at gmail.com> wrote:
Hi everyone,
When dealing with errors, sometimes I want to run a bunch of code
an error occurs.
For now I usually use a structure such as:
res <- tryCatch(expr, error = function(cond) cond) # or try(expr)
if (inherits(res, ?error?)) # or inherits(res, ?try-error?)
# a bunch of code
I though it would be useful to have a function that does this
naturally, so I came up with the attached function.
I would be glad to hear your insights and if you think it would make
sense to add this function to R.
Best regards,
Ernest