Is it possible to overwrite any function to customize the default error messages of R?

# Create custom error messages

Hi @aguerodev. You may use `tryCatch`

as the following link.

http://www.win-vector.com/blog/2012/10/error-handling-in-r/

The idea is to be able to overwrite the error messages to make them more friendly for my students.

One thing you can try is "monkey patching," where you create a new function with the same name. This is pretty easy in R. For your case, the new function would wrap a `tryCatch`

around a call to the original function, look for certain error messages, and raise custom errors when it sees them.

For example, these `lm`

error messages aren't helpful for new users:

```
lm(goblins ~ pirates, data = mtcars)
# Error in eval(predvars, data, env) : object 'goblins' not found
lm(BJsales)
# Error in formula.default(object, env = baseenv()) : invalid formula
```

A replacement with better messages:

```
new_lm <- function(...) {
# Record the parameter values as written
data_text <- deparse(substitute(data))
formula_text <- deparse(substitute(formula))
tryCatch(
# Use :: notation to make sure we use the original version
stats::lm(formula = formula, data = data, ...),
error = function(err) {
msg <- conditionMessage(err)
if (grepl("object '.*' not found", msg)) {
new_msg <- gsub(
"object ('.*') not found",
paste("\\1 is not in", data_text),
msg
)
stop(new_msg)
}
if (grepl("invalid formula", msg)) {
new_msg <- paste0(
"'", formula_text, "' is not a valid formula.\n",
"See ?lm or ?formula for help."
)
stop(new_msg)
}
stop(err)
}
)
}
# Give it named parameters instead of just "..."
# These are helpful with most IDEs
formals(new_lm) <- formals(lm)
lm <- new_lm
lm(goblins ~ pirates, data = mtcars)
# Error in value[[3L]](cond) : 'goblins' is not in mtcars
lm(BJsales)
# Error in value[[3L]](cond) : 'BJsales' is not a valid formula.
# See ?lm or ?formula for help.
```

You can put your monkey-patch functions in a package for the students.

For those who want to make this more automated, I tried putting the `deparse(substitute(x))`

inside a loop over all parameters. But environments are wonky. If anyone can do this, I'd like to see the solution. If anyone can do this *elegantly*, I'd *love* to see the solution.

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