'local-time' 1 Introduction 1.1 Portability 2 Public API 2.1 Types 2.2 Timezones 2.3 Creating 'timestamp' Objects 2.4 Querying 'timestamp' Objects 2.5 Manipulating Date and Time Values 2.6 Parsing and Formatting 2.7 Clocks 3 Other Features 3.1 Reader Macros 3.2 Support for non-Gregorian Calendars 4 References Index 'local-time' ************ Copyright (C) 2012 Daniel Lowe Copyright (C) 2012 Attila Lendvai This manual describes the 'local-time' Common Lisp library which is based on Erik Naggum's _The Long, Painful History of Time_ [NaggumPaper] paper. 1 Introduction ************** The 'local-time' library is a Common Lisp library for the manipulation of dates, times and intervals. It was originally based almost entirely upon Erik Naggum's paper _The Long Painful History of Time_ [NaggumPaper]. Many of the core concepts originated from this paper, such as the seperation of days and seconds, the choice of 2000-03-01 as the standard epoch, and the timestring format. 1.1 Portability =============== This implementation assumes that time zone information is stored in the tzfile format. The default timezone is loaded from /etc/localtime. On non-POSIX systems, this will certainly give different results than the system time handling. local-time currently supports subsecond precision clocks with allegro, cmucl, sbcl, abcl, and non-Windows ccl. All others will be able to retrieve the time with second precision using 'get-universal-time'. You may add support for your own implementation by implementing the clock generic protocol documented here. 2 Public API ************ 2.1 Types ========= It's a good idea to treat all values as immutable objects. 'local-time' will not modify any object it was given unless explicitly asked to by the ':into' keyword argument. -- Class: timestamp day sec nsec 'timestamp' values can represent either a _date_, a _daytime_ or a _time_ value. It has the following slots: (defclass timestamp () ((day :type integer) (sec :type integer) (nsec :type (integer 0 999999999)))) The following constraints apply to the specific types: * _date_: must have a +UTC-ZONE+ timezone and the SEC slot must be the first second of a day; In other words, the time elements of the 'timestamp' value must have their least possible values. * _time_: the DAY slot must be zero. -- Struct: timezone path name loaded 'timezone' objects represent timezones - local and political modifications to the time representation. Timezones are responsible for storing offsets from GMT, abbreviations for different sub-timezones, and the times each sub-timezone is to be in effect. 2.2 Timezones ============= -- Default: *default-timezone* The variable *DEFAULT-TIMEZONE* contains the timezone that will be used by default if none is specified. It is loaded from _/etc/localtime_ when the library is loaded. If _/etc/localtime_ is not present, it will default to UTC. -- Constant: +utc-zone+ The variable +UTC-ZONE+ contains a timezone corresponding to UTC. -- Macro: define-timezone zone-name zone-file &key (load nil) Define ZONE-NAME (a symbol or a string) as a new timezone, lazy-loaded from ZONE-FILE (a pathname designator relative to the zoneinfo directory on this system. If LOAD is true, load immediately. -- Function: find-timezone-by-location-name name Returns the timezone found at the location name (such as 'US/Eastern'). 'reread-timezone-repository' must be called before this function is used. -- Function: reread-timezone-repository &key (timezone-repository *default-timezone-repository-path*) Walks the current repository, reading all tzinfo files updating indexes. The default timezone repository is set to the zoneinfo/ directory of the local-time system. 2.3 Creating 'timestamp' Objects ================================ -- Function: universal-to-timestamp universal &key (nsec 0) Produces a 'timestamp' instance from the provided universal time UNIVERSAL. Universal time is defined in the Common Lisp Specification as the number of seconds since 1900-01-01T00:00:00Z. -- Function: unix-to-timestamp unix &key (nsec 0) Produces a 'timestamp' instance from the provided unix time UNIX. Unix time is defined by POSIX as the number of seconds since 1970-01-01T00:00:00Z. -- Function: now Produces a 'timestamp' instance with the current time. Under sbcl, the new timestamp will be precise to the microsecond. Otherwise, the precision is limited to the second. -- Function: today Produces a 'timestamp' instance that corresponds to today's date, which is the midnight of the current day in the UTC zone. -- Function: encode-timestamp nsec sec minute hour day month year &key timezone offset into Returns a new 'timestamp' instance corresponding to the specified time elements. The OFFSET is the number of seconds offset from UTC of the locale. If OFFSET is not specified, the offset will be guessed from the TIMEZONE. If a 'timestamp' is passed as the INTO argument, its value will be set and that 'timestamp' will be returned. Otherwise, a new 'timestamp' is created. -- Macro: make-timestamp &key :day :sec :nsec Expands to an expression that creates an instance of a 'timestamp' exactly as specified. -- Macro: clone-timestamp timestamp Expands to an expression that creates another copy of TIMESTAMP that is 'timestamp=' to it. 2.4 Querying 'timestamp' Objects ================================ -- Function: day-of timestamp Returns the day component of TIMESTAMP. Although Naggum's paper specifies that the day should be a signed fixnum, it is left unbounded for flexibility reasons. -- Function: sec-of timestamp Returns the 'seconds' component of the time. Valid values for the seconds range from 0 to 86399. -- Function: nsec-of timestamp Returns the 'microseconds' component of the time. Valid values for the nanoseconds range from 0 to 999999999. -- Function: timestamp-to-universal timestamp This returns the date/time specified in TIMESTAMP encoded as the number of seconds since January 1st, 1900 12:00am UTC. -- Function: timestamp-to-unix timestamp This returns the date/time specified in TIMESTAMP encoded as the number of seconds since January 1st, 1970 12:00am UTC. It corresponds with the time received from the POSIX call 'time()'. -- Function: timestamp-subtimezone timestamp timezone Returns as multiple values the time zone applicable at the given time as the number of seconds east of UTC, a boolean daylight-saving-p, and the customary abbreviation of the timezone. -- Macro: with-decoded-timestamp (&key nsec sec minute hour day month year day-of-week daylight-p timezone) timestamp &body body This macro binds variables to the decoded elements of TIMESTAMP. The timezone argument is used for decoding the timestamp, and is not bound by the macro. The value of DAY-OF-WEEK starts from 0 which means Sunday. -- Function: decode-timestamp timestamp Returns the decoded time as '(values ns ss mm hh day month year day-of-week daylight-saving-time-p timezone-offset timezone-abbreviation)'. -- Function: timestamp< time-a time-b -- Function: timestamp<= time-a time-b -- Function: timestamp> time-a time-b -- Function: timestamp>= time-a time-b -- Function: timestamp= time-a time-b -- Function: timestamp/= time-a time-b These comparison functions act like their string and char counterparts. -- Function: timestamp-minimum timestamp &rest timestamps Returns the earliest timestamp passed to it. -- Function: timestamp-maximum timestamp &rest timestamps Returns the latest timestamp passed to it. -- Function: timestamp-day-of-week timestamp This returns the index of the day of the week, starting at 0 which means Sunday. Note: "Day of the week" is ambigous and locale dependent. -- Function: universal-to-timestamp timestamp Returns the UNIVERSAL-TIME corresponding to TIMESTAMP. Note: Subsecond precision is not preserved. -- Function: timestamp-millennium timestamp &key timezone -- Function: timestamp-century timestamp &key timezone -- Function: timestamp-decade timestamp &key timezone Returns the ordinal millennium, century or decade upon which the timestamp falls. Ordinal time values start at 1, so the (timestamp-century (now)) will return 21. -- Function: timestamp-year timestamp &key timezone -- Function: timestamp-month timestamp &key timezone -- Function: timestamp-day timestamp &key timezone -- Function: timestamp-hour timestamp &key timezone -- Function: timestamp-minute timestamp &key timezone -- Function: timestamp-second timestamp &key timezone -- Function: timestamp-millisecond timestamp &key timezone -- Function: timestamp-microsecond timestamp &key timezone -- Function: timestamp-microsecond timestamp &key timezone Returns the decoded part of the timestamp. 2.5 Manipulating Date and Time Values ===================================== -- Function: timestamp+ time amount unit -- Function: timestamp- time amount unit Add or subtract the AMOUNT to the TIME using the specified UNIT. UNIT may be one of ( ':nsec' ':sec' ':minute' ':hour' ':day' ':month' ':year'). The value of the parts of the timestamp of higher resolution than the UNIT will never be touched. If you want a precise number of seconds from a time, you should specify the offset in seconds. -- Function: timestamp-maximize-part timestamp part &key offset timezone into Returns a timestamp with its parts maximized up to PART. PART can be any of (:nsec :sec :min :hour :day :month). If INTO is specified, it will be modified and returned, otherwise a new timestamp will be created. -- Function: timestamp-minimize-part timestamp part &key offset timezone into Returns a timestamp with its parts minimized up to PART. PART can be any of (:nsec :sec :min :hour :day :month). If INTO is specified, it will be modified and returned, otherwise a new timestamp will be created. -- Macro: adjust-timestamp timestamp &body changes Alters various parts of TIMESTAMP, given a list of changes. The changes are in the format '(offset part value)' and '(set part value)'. ;; Return a new timestamp value that points to the previous Monday (adjust-timestamp (today) (offset :day-of-week :monday)) ;; Return a new timestamp value that points three days ahead from now (adjust-timestamp (today) (offset :day 3)) Keep in mind that 'adjust-timestamp' is not a mere setter for fields but instead it handles overflows and timezone conversions as expected. Also note that it's possible to specify multiple commands. The list of possible places to manipulate are: ':nsec' ':sec' ':sec-of-day' ':minute' ':hour' ':day' ':day-of-month' ':month' ':year'. -- Macro: adjust-timestamp! timestamp &body changes Just like 'adjust-timestamp', but instead of returning a freshly constructed value, it alters the provided TIMESTAMP value (and returns it). -- Function: timestamp-whole-year-difference time-a time-b Returns the number of whole years elapsed between TIME-A and TIME-B. Note: This is useful for calculating anniversaries and birthdays. -- Function: days-in-month month year Returns the number of days in a given month of the specified year. 2.6 Parsing and Formatting ========================== -- Constant: +iso-8601-format+ The constant +ISO-8601-FORMAT+ is bound to a description of the ISO 8601 format. An output with this format will look like this: '2008-03-01T19:42:34.608506+01:00'. This is the default format for the 'format-timestring' function. -- Constant: +asctime-format+ The constant +ASCTIME-FORMAT+ is bound to a format mirroring the output of the POSIX asctime() function. An output with this format will look like this: 'Sat Mar 1 19:42:34 2008'. -- Constant: +rfc-1123-format+ The constant +RFC-1123-FORMAT+ is bound to a description of the format defined in RFC 1123 for Internet timestamps. An output with this format will look like this: 'Sat, 01 Mar 2008 19:42:34 -0500'. -- Constant: +iso-week-date-format+ The constant +ISO-WEEK-DATE-FORMAT+ is bound to a description of the ISO 8601 Week Date format. An output with this format will look like this: '2009-W53-5'. -- Function: parse-timestring timestring &key (start 0) end (fail-on-error t) (offset 0) Parses a timestring and returns the corresponding 'timestamp'. Parsing begins at START and stops at the END position. If there are invalid characters within 'timestring' and FAIL-ON-ERROR is 'T', then an 'invalid-timestring' error is signaled, otherwise 'NIL' is returned. If there is no timezone specified in 'timestring' then OFFSET is used as the default timezone offset (in seconds). -- Function: format-timestring (destination timestamp &key (format +iso-8601-format+) (timezone *default-timezone*)) Constructs a string representation of TIMESTAMP according to FORMAT and returns it. If destination is 'T', the string is written to '*standard-output*'. If destination is a stream, the string is written to the stream. FORMAT is a list containing one or more of strings, characters, and keywords. Strings and characters are output literally, while keywords are replaced by the values here: ':year' *year ':month' *numeric month ':day' *day of month ':weekday' *numeric day of week, starting from 0 which means Sunday ':hour' *hour ':min' *minutes ':sec' *seconds ':msec' *milliseconds ':usec' *microseconds ':nsec' *nanoseconds ':iso-week-year' *year for ISO week date (can be different from regular calendar year) ':iso-week-number' *ISO week number (i.e. 1 through 53) ':iso-week-day' *ISO compatible weekday number (i.e. monday=1, sunday=7) ':ordinal-day' day of month as an ordinal (e.g. 1st, 23rd) ':long-weekday' long form of weekday (e.g. Sunday, Monday) ':short-weekday' short form of weekday (e.g. Sun, Mon) ':minimal-weekday' minimal form of weekday (e.g. Su, Mo) ':long-month' long form of month (e.g. January, February) ':short-month' short form of month (e.g. Jan, Feb) ':hour12' hour on a 12-hour clock ':ampm' am/pm marker in lowercase ':gmt-offset' the gmt-offset of the time, in +00:00 form ':gmt-offset-or-z' like :gmt-offset, but is Z when UTC ':gmt-offset-hhmm' like :gmt-offset, but in +0000 form ':timezone' timezone abbrevation for the time Elements marked by * can be placed in a list in the form: (:keyword padding &optional (padchar #\0)) The string representation of the value will be padded with the padchar. You can see examples by examining the values in +ISO-8601-FORMAT+, +ASCTIME-FORMAT+, and +RFC-1123-FORMAT+. Produces on STREAM the timestring corresponding to the TIMESTAMP with the given options. If STREAM is 'nil', only returns a string containing what would have been the output. If STREAM is 't', prints the string to *STANDARD-OUTPUT*. Example output: LOCAL-TIME> (format-timestring nil (now)) "2008-03-01T19:42:34.608506+01:00" -- Function: format-rfc3339-timestring (destination timestamp &key omit-date-part omit-time-part omit-timezone-part (use-zulu t)) Formats the time like format-timestring, but in RFC 3339 format. The options control valid options in the RFC. 2.7 Clocks ========== -- Default: *clock* The *clock* special variable and the following generic functions are exposed so that applications may re-define the current time or date as required. This can be used for testing or to support alternate clocks. The currently supported values are: * 't' - Use the standard system clock with no adjustments * 'leap-second-adjusted' - The system clock, adjusted for leap seconds using the information in *default-timezone*. -- Function: clock-now (clock) Specialize this generic function to re-define the present moment -- Function: clock-today (clock) Specialize this generic function to re-define the present day 3 Other Features **************** 3.1 Reader Macros ================= -- Function: enable-read-macros Adds @TIMESTRING and #@UNIVERSAL-TIME as reader macros. 3.2 Support for non-Gregorian Calendars ======================================= -- Function: astronomical-julian-date timestamp Returns the julian date of the date portion of TIMESTAMP. -- Function: astronomical-julian-date timestamp Returns the modified julian date of the date portion of TIMESTAMP. 4 References ************ * [NaggumPaper] Erik Naggum. _The Long Painful History of Time_ , 1999. Index ***** * Menu: * *clock*: Clocks. (line 463) * *default-timezone*: Timezones. (line 90) * *default-timezone* <1>: Timezones. (line 90) * +asctime-format+: Parsing and Formatting. (line 343) * +asctime-format+ <1>: Parsing and Formatting. (line 343) * +iso-8601-format+: Parsing and Formatting. (line 336) * +iso-8601-format+ <1>: Parsing and Formatting. (line 336) * +iso-week-date-format+: Parsing and Formatting. (line 355) * +iso-week-date-format+ <1>: Parsing and Formatting. (line 355) * +rfc-1123-format+: Parsing and Formatting. (line 349) * +rfc-1123-format+ <1>: Parsing and Formatting. (line 349) * +utc-zone+: Timezones. (line 97) * +utc-zone+ <1>: Timezones. (line 97) * adjust-timestamp: Manipulating Date and Time Values. (line 295) * adjust-timestamp!: Manipulating Date and Time Values. (line 316) * astronomical-julian-date: Other Features. (line 497) * clone-timestamp: Creating timestamp Objects. (line 162) * day-of: Querying timestamp Objects. (line 170) * days-in-month: Manipulating Date and Time Values. (line 329) * decode-timestamp: Querying timestamp Objects. (line 211) * define-timezone: Timezones. (line 101) * enable-read-macros: Other Features. (line 490) * encode-timestamp: Creating timestamp Objects. (line 147) * find-timezone-by-location-name: Timezones. (line 108) * format-rfc3339-timestring: Parsing and Formatting. (line 454) * format-timestring: Parsing and Formatting. (line 373) * make-timestamp: Creating timestamp Objects. (line 157) * modified-julian-date: Other Features. (line 501) * now: Creating timestamp Objects. (line 136) * nsec-of: Querying timestamp Objects. (line 181) * parse-timestring: Parsing and Formatting. (line 361) * reread-timezone-repository: Timezones. (line 114) * sec-of: Querying timestamp Objects. (line 176) * timestamp: Types. (line 60) * timestamp+: Manipulating Date and Time Values. (line 269) * timestamp-: Manipulating Date and Time Values. (line 269) * timestamp-century: Querying timestamp Objects. (line 246) * timestamp-day: Querying timestamp Objects. (line 254) * timestamp-day-of-week: Querying timestamp Objects. (line 235) * timestamp-decade: Querying timestamp Objects. (line 246) * timestamp-hour: Querying timestamp Objects. (line 254) * timestamp-maximize-part: Manipulating Date and Time Values. (line 279) * timestamp-maximum: Querying timestamp Objects. (line 231) * timestamp-microsecond: Querying timestamp Objects. (line 254) * timestamp-millennium: Querying timestamp Objects. (line 246) * timestamp-millisecond: Querying timestamp Objects. (line 254) * timestamp-minimize-part: Manipulating Date and Time Values. (line 287) * timestamp-minimum: Querying timestamp Objects. (line 227) * timestamp-minute: Querying timestamp Objects. (line 254) * timestamp-month: Querying timestamp Objects. (line 254) * timestamp-second: Querying timestamp Objects. (line 254) * timestamp-subtimezone: Querying timestamp Objects. (line 197) * timestamp-to-universal: Querying timestamp Objects. (line 186) * timestamp-to-unix: Querying timestamp Objects. (line 191) * timestamp-whole-year-difference: Manipulating Date and Time Values. (line 322) * timestamp-year: Querying timestamp Objects. (line 254) * timestamp/=: Querying timestamp Objects. (line 217) * timestamp<: Querying timestamp Objects. (line 217) * timestamp<=: Querying timestamp Objects. (line 217) * timestamp=: Querying timestamp Objects. (line 217) * timestamp>: Querying timestamp Objects. (line 217) * timestamp>=: Querying timestamp Objects. (line 217) * today: Creating timestamp Objects. (line 142) * universal-to-timestamp: Creating timestamp Objects. (line 124) * universal-to-timestamp <1>: Querying timestamp Objects. (line 241) * unix-to-timestamp: Creating timestamp Objects. (line 130) * with-decoded-timestamp: Querying timestamp Objects. (line 203)