Subtract time

[tommyjcarpenter]

Is there a negative or inverse of add_time?

[grantwinney]

There's no function for it in this library, but you could just use negative numbers:

% show current time
> calendar:local_time().
{{2017,7,7},{15,5,42}}

% subtract 2 hours, 3 minutes, 4 seconds
> iso8601:add_time(calendar:local_time(), -2, -3, -4).
{{2017,7,7},{13,2,38}}

You could even define your own function for convenience:

Subtract = fun(Datetime, H, M, S) -> iso8601:add_time(Datetime, -H, -M, -S) end.

% show current time
> calendar:local_time().
{{2017,7,7},{15,10,39}}

% subtract 2 hours, 3 minutes, 10 seconds
> Subtract(calendar:local_time(), 2, 3, 10).
{{2017,7,7},{13,7,29}}

[oubiwann]

We can definitely add this.