YAW(N)S

Last post on this subject for now, hopefully, since even I’m getting bored of it. Just for the sake of completeness, I did the ISO date formatting ‘properly’, as follows:

w3cdtf(GregSecs) ->
	Date=calendar:gregorian_seconds_to_datetime(GregSecs),
	[UDate|_]=calendar:local_time_to_universal_time_dst(Date),
	USecs=calendar:datetime_to_gregorian_seconds(UDate),
	{{Y, M, D},{HH, MM, SS}} = Date,
	io_lib:format("~4..0b-~2..0b-~2..0bT~2..0b:~2..0b:~2..0b~s",
		[Y,M,D,HH,MM,SS,tzid(GregSecs-USecs)]).
 
tzid(Secs) when Secs==0 ->
	"Z";
tzid(Secs) ->
	{HH,MM,_}=calendar:seconds_to_time(abs(Secs)),
	io_lib:format("~c~2..0b:~2..0b",
		[case Secs >= 0 of false -> $-; true -> $+ end,HH,MM]).

As well as being shorter and clearer still, it doesn’t use the calendar:time_difference like the original did. That’s good because not only is that function very silly, it turns out it is marked as obsolete in the documentation. I suspect those two points are not unrelated.

Anyway, I’ll probably give the above some more rigourous testing and submit a patch. It may seem rather trivial, but actually it was a good exercise in getting to know Erlang a bit better. Half an hour of practical problem is usually worth ten of reading TFM.