On Mon, Apr 27, 2020 at 2:38 AM Tim Hanson <tbh...@gmail.com> wrote: > > hi, I've installed and am trying out > > Gregor: a date and time library for Racket > > and find it to be very powerful and useful.
Thanks! > > In my current application (digging through mail headers) I'm wondering > whether there is a way to test whether a given date-time format matches > without using exceptions. (I assume that would generally be more efficient > than catching exceptions.) > [...] > > I thought I'd check here: > - does this seem like a reasonable idea? It does to me. > - is mine an unusual use case and most folks know what format to expect and > the exception approach is fine? Good question. If you're expecting dates/times to come in a variety of formats, I can see why you'd want to try out a few of them. And that is made more difficult by having these functions raise exceptions. So I think it would have been wiser to make these functions behave the way you've indicated. Or maybe partially so...? The exceptions that occur during a parse can come from three (I hope I counted them all) three distinct sources: - Your pattern may be lexically invalid (e.g., `(parse-datetime "2/29/2000" "M/f/y")`.) - Your pattern may fail to match the input (e.g., `(parse-datetime "2/29/2000" "MMM/d/y")`.). - Your pattern may match the input, but the interpretation of the input as a date, datetime, etc. may refer to a date that does not exist in the Gregorian calendar (e.g., `(parse-datetime "2/29/1999" "M/d/y")` or a date-time that does not exist in a local time zone (e.g., a time between 2-3 am during a transition to Daylight Saving Time from Standard Time in the U.S.). I think the first of these would definitely remain an exception. The second is the most obvious candidate for returning #f instead of raising. The third is (to me) the least obvious. > - is there perhaps an elegant way for me to test with a regular expression > first rather than adding this function to Gregor? That would depend on the particular formats you're expecting. > > Cheers, > > Tim -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAKfDxxzFVQ43L3%3D_61VGTEuoVn-7rZvG5YmHtRO-sw2wM4Xp8A%40mail.gmail.com.
