If I do understand the Factor code
ymd>timestamp correctly uses gmt but timestamp>ymd uses local time.
So in Germany in summer
today dup timestamp>ymd ymd>timestamp time- duration>hours .
prints -2
Does that mean there is a bug in timestamp>ymd ?
I my application I want to use date strings of the local time. So I am
thinking about local time versions. To get words that are not very long
I replaced ymd by YMD. timestamp>YMD forgets the gmt-offset and
YMD>timestamp expects a local date string and makes a timestamp with
timezone information like the words yesterday and today.
( YMD>timestamp replaces local-ymd>timestamp from yesterday )
USING:
calendar calendar.format calendar.format.macros
io.streams.string typed
;
IN: localDateString
TYPED: timestamp>YMD ( timestamp: timestamp -- str )
[ { YYYY "-" MM "-" DD } formatted ] with-string-writer
;
: YMD>timestamp ( str -- timestamp )
[ read-ymd 0 0 0 gmt-offset-duration <timestamp> ]
with-string-reader
;
Now
today >gmt "2014-08-31" YMD>timestamp time- duration>days .
today "2014-08-31" YMD>timestamp time- duration>days .
today dup timestamp>YMD YMD>timestamp time- duration>hours .
print 4 4 0 respectively which is what I wanted.
> Oh, I see -- you want to compare a date in local time with a date in
> GMT without considering the timezone difference.
>
> Your solution seems okay, albeit a little complicated by trying to
> undo the notion of timezones. Perhaps as you play with it a bit ,
> you might have some idea of improvements to the API. We were trying
> to preserve timezone information as much as possible, so for example
> as you convert a YMD to a timestamp, it assumes GMT. Later, as you
> use it, the timezone is included for time differences and other words.
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