[Haskell-cafe] Can't do basic time operations with System.Time

[John Goerzen]

On Fri, Jan 21, 2005 at 02:55:31PM -0000, Simon Marlow wrote:
> Have you seen this, BTW:
> 
>   http://www.haskell.org/~simonmar/time/NewTime.html

Ah.  I think I found several discussions in reply to that but never did
actually track down that URL.

I'll take a look.

> > timelocal :: CalendarTime -> IO Integer
> 
> This looks useful, given that it was what you wanted and it isn't
> already provided.  I'd prefer to drop it into the existing library, and
> have it return a ClockTime, though.  Perhaps:

I did it as it was because the standard defined ClockTime to be opaque.
Obviously it's not in fptools, so your way is fine there.  But the
method of getting seconds out of it should be documented, or a simple
function could be added:

-- | Convert a ClockTime to a POSIX seconds-since-epoch representation.
clockTimeToEpochTime :: ClockTime -> Integer
clockTimeToEpochTime (TOD x _) = x

>   -- | converts the given CalendarTime into a ClockTime,
>   -- ignoring the ctTZ field of CalendarTime and instead 
>   -- using the prevailing local timezone (including daylight
>   -- savings adjustments) at the given time.
>   localTimeToClockTime :: CalendarTime -> IO ClockTime
> 
> that's more or less a direct interface to mktime().

That would be fine too (you might also note that ctIsDST is ignored).

-- John