Re: Concerning Time.TimeDiff

On 2003-06-18 at 15:19+0200 ketil@ii.uib.no (Ketil Z. Malde) wrote:

"Simon Marlow" writes:

...

- calendarTimeToClockTime now returns a Maybe.

Okay, this is perhaps more "functional", but is it really what I want? Wouldn't an illegal calendarTime often be a bug in the code, and if so, isn't it better to just crash? I don't much care for wrapping things in Maybe, could we have an 'isCalendarTimeValid' instead (in order to verify values that aren't static)?

I.e., isn't this

foo ct | isCalendarTimeValid ct -> ...calendarTimeToClockTime ct... | otherwise -> error ...

as useful as this

foo ct = case calendarTimeToClockTime ct of Just t -> .... Nothing -> error ...

? And of course cleaner in the cases where you *don't* need to check?

If you want to write in that style, there's nothing to stop you writing wrappers to do it. You can write crashableCalendarTimeToClockTime (which would look much like foo above. I think that standard things in Haskell should not use crashing as a solution if it can possible be avoided. Best would be if the type system could enforce validity of calendar times and restrict the possibility of errors to conversion from strings and suchlike. Given the peculiar constraints on calender times this is too much to ask, however. Jón -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk 31 Chalmers Road jf@cl.cam.ac.uk Cambridge CB1 3SZ +44 1223 570179 (after 14:00 only, please!)