7 The Date Module
7.3 Representing durations
Date/time intervals, called durations, are modeled in a style quite similar to that of SQL. There are two, effectively disjoint, classes of duration: one with a resolution of months (for example, 3 years, 2 months) and the other with a resolution of microseconds (for example, 50 days, 6 hours, 23 minutes). The first is <year/month-duration> and the second <day/time-duration>.
An important distinction between <day/time-duration> and <year/month-duration> is that a given instance of <day/time-duration> is always a fixed unit of a fixed length, whereas a <year/month-duration> follows the vagaries of the calendar. So if you have a <date> that represents, for example, the 5th of some month, adding a <year/month-duration> of 1 month to that will always take you to the 5th of the following month, whether that is an interval of 28, 29, 30, or 31 days.
Sealed abstract instantiable class
- This class is the used to represent durations. It is a subclass of
<number>, and it has two subclasses, described below.
Sealed class
- Represents durations in units of calendar months. It is a subclass of
<duration>.
Sealed class
- Represents durations in units of microseconds. It is a subclass of
<duration>.
The following functions and methods are available for creating durations, and decoding them into their constituent integer parts.
encode-year/month-durationFunction
encode-year/month-duration years months => duration
- Creates an instance of
<year/month-duration>.
Function
encode-day/time-duration days hours minutes seconds microseconds => duration
- Creates an instance of
<day/time-duration>.
Sealed generic function
decode-duration duration => #rest components
- Decodes an instance of
<duration>into its constituent parts. There are methods for this generic function that specialize on<year/month-duration>and<day/time-duration>respectively, as described below.
Sealed method
decode-duration duration => years months
- Decodes an instance of
<year/month-duration>into its constituent parts.
Sealed method
decode-duration duration => days hours minutes seconds microseconds
- Decodes an instance of
<day/time-duration>into its constituent parts.