On 09/10/2023 7:57 p.m., Michael Chirico via R-devel wrote:
It will be useful to package authors trying to validate input which is supposed to be a valid regular expression.As near as I can tell, the only way we can do so now is to run any regex function and check for the warning and/or condition to bubble up: valid_regex <- function(str) { stopifnot(is.character(str), length(str) == 1L) !inherits(tryCatch(grepl(str, ""), condition = identity), "condition") } That's pretty hefty/inscrutable for such a simple validation. I see a variety of similar approaches in CRAN packages [1], all slightly different. It would be good for R to expose a "canonical" way to run this validation.
I think currently we do as.character(str) (or some equivalent), so the test shouldn't require str to be a character to start. For example, this is currently valid code:
grepl(1, "abc123") It's not great style, but shouldn't generate an error. Duncan Murdoch
At root, the problem is that R does not expose the regex compilation routines like 'tre_regcomp', so from the R side we have to resort to hacky approaches. Things get slightly complicated by encoding/useBytes modes (tre_regwcomp, tre_regncomp, tre_regwncomp, tre_regcompb, tre_regncompb; all in tre.h), but all are already present in other regex routines, so this is doable. Exposing a function to compile regular expressions is common in other languages, e.g. Go [2], Python [3], JavaScript [4]. [1] https://github.com/search?q=lang%3AR+%2Fis%5Ba-zA-Z0-9._%5D*reg%5Ba-zA-Z0-9._%5D*ex.*%28%3C-%7C%3D%29%5Cs*function%2F+org%3Acran&type=code [2] https://pkg.go.dev/regexp#Compile [3] https://docs.python.org/3/library/re.html#re.compile [4] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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