library(date)

library(date) is a time-stamp package.

• Dates are records of the form date(Year, Month, Day).
• Times are records of the form time(Hour, Minute, Second).
• Datimes are records of the form date(Year, Month, Day, Hour, Minute, Second).
• "When" values are 32-bit time-stamps representing the number of seconds since the beginning of January 1st 1970, represented as integers.

The parameter ranges are

These parameter ranges are compatible with the library function localtime(3). Note that the range for months is not what you might expect.

The predicates provided are:

• now(?When)
• date(-DateNow)
• date(+When, -DateThen)
• time(-TimeNow)
• time(+When, -TimeThen)
• datime(-DatimeNow)
• datime(+When, -DatimeThen)
• datime(?Datime, ?Date, ?Time)
• date_and_time(-DateNow, -TimeNow)
• date_and_time(+When, -DateThen, -TimeThen)
• portray_date(+TimeStamp)
• time_stamp(+Format, -TimeStamp)
• time_stamp(+When, +Format, -TimeStamp)

For example,

     | ?- date(X), portray_date(X).
     11-Jan-90
     X = date(90,0,11)
     

Note that if you want both the current date and time, you should call either datime/1 or date_and_time/2. It is an error to obtain the date and time in separate calls, because midnight could intervene and put you nearly 24 hours out.

Dates and datimes are also returned by directory_property/3 and file_property/3 (see library(directory)). All these records can be compared using term comparison.

The predicates time_stamp/[2,3] provide a way of creating a time-stamp atom using a special kind of format string. For example,

     | ?- time_stamp('%W, %d %M %y',Date).
     
     Date = 'Thursday, 11 January 1990'
     

The details of the format strings are explained in a comment in the sources. Please note that, in the interests of internationalization, time_stamp/[2,3] are likely to be superseded in a future release by something based on the ANSI C operation strftime(3). The other predicates in this package will not change at that time.