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srfi-19

Time Data Types and Procedures

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srfi-19
Documentation
Usage
Examples
Notes
Bugs and Limitations
Requirements
Author
Version history
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Documentation

This is a Chicken port of SRFI-19. This document only describes the extensions. For the SRFI-19 API see SRFI-19.

Core Procedures

The core procedures are those pertaining to time, date, and timezone:

(require-extension srfi-19-core)

The core procedures can be separately accessed:

(require-extension srfi-19-time)

(require-extension srfi-19-date)

(require-extension srfi-19-timezone)

(require-extension srfi-19-io)

SRFI-19 Document Changes

The nanosecond time object element is an integer between 0 and 999,999,999 inclusive. (The SRFI-19 document mis-states the value.)

A tz-offset value follows ISO 8601; positive for east of UTC, and negative for west. This is the opposite of the POSIX TZ environment variable.

Where the SRFI-19 document states a tz-offset argument a timezone-components object is also legal.

The string->date procedure allows the template-name argument to be optional. When missing the locale's date-time-format string is used. The supplied locale bundle's strings are invertible.

make-date

[procedure] (make-date NANOSECOND SECOND MINUTE HOUR DAY MONTH YEAR [ZONE-OFFSET [TZ-NAME [DST-FLAG]]]) -> date

Same as SRFI-19 except for the optional parameters and allowing a timezone-components object for the ZONE-OFFSET.

The ZONE-OFFSET is an integer or timezone-components. Default is the (timezone-locale-offset), the current locale timezone offset.

The TZ-NAME is a string or #f, and is the timezone name. Default is #f.

The DST-FLAG is a boolean, and indicates whether Day Saving TIme (or Summer Time) is active. Default is #f.

When the ZONE-OFFSET is a timezone-components object the TZ-NAME and DST-FLAG are pulled from the timezone-components, unless explicitly supplied.

read-leap-second-table

[procedure] (read-leap-second-table FILENAME)

Sets the leap second table from the specified FILENAME.

The file format is the same as the "tai-utc.dat" file in the distribution. Provided by the U.S. Naval Observatory.

leap-year?

[procedure] (leap-year? DATE) -> boolean

Does the specified DATE fall on a leap year?

The DATE may be a numeric year or a date object.

SRFI-18 Time

Note that the SRFI-18 identifiers time?, current-time, seconds->time, time->seconds, milliseconds->time, and time->milliseconds are in conflict with those of SRFI-19.

time->srfi-18-time

[procedure] (time->srfi-18-time TIME) -> srfi-18#time

Converts a SRFI-19 time object to a SRFI-18 time object. The conversion is really only meaningful for time-duration, but any time-type is accepted.

srfi-18-time->time

[procedure] (srfi-18-time->time TIME) -> srfi-19#time

Converts a SRFI-18 time object into a SRFI-19 time-duration object.

Object Printing

time-record-printer-format

[procedure] (time-record-printer-format [FORM]) -> (or symbol boolean)

FORM is 'srfi-10 or '#f.

date-record-printer-format

[procedure] (date-record-printer-format [FORM]) -> (or symbol boolean)

FORM is 'srfi-10 or '#f.

Time Conversion

seconds->time

[procedure] (seconds->time SECONDS [TIME-TYPE time-duration]) -> time

Converts a SECONDS value, may be fractional, into a TIME-TYPE time object.

seconds->date

[procedure] (seconds->date SECONDS [TIMEZONE-INFO #t]) -> date

Converts a SECONDS value, which may be fractional, into a date object. The TIMEZONE-INFO is #t for the local timezone, #f for the utc timezone, or a timezone-components object.

SECONDS is relative to 00:00:00 January 1, 1970 UTC.

time->nanoseconds

[procedure] (time->nanoseconds TIME) -> integer

Returns the TIME object value as a nanoseconds value.

nanoseconds->time

[procedure] (nanoseconds->time NANOSECONDS [TIME-TYPE time-duration]) -> time

Returns the NANOSECONDS value as a time TIME-TYPE object.

nanoseconds->seconds

[procedure] (nanoseconds->seconds NANOSECONDS) -> number

Returns the NANOSECONDS value as an inexact seconds value.

time->milliseconds

[procedure] (time->milliseconds TIME) -> integer

Returns the TIME object value as a milliseconds value.

milliseconds->time

[procedure] (milliseconds->time MILLISECONDS [TIME-TYPE time-duration]) -> time

Returns the MILLISECONDS value as a time TIME-TYPE object.

milliseconds->seconds

[procedure] (milliseconds->seconds MILLISECONDS) -> number

Returns the MILLISECONDS value as an inexact seconds value.

time->date

[procedure] (time->date TIME) -> date

Returns the TIME object value as a date. A shorthand for the (time-*->date...) procedures.

time->julian-day

[procedure] (time->julian-day TIME) -> rational

Returns the julian day for the TIME object.

time->modified-julian-day

[procedure] (time->modified-julian-day TIME) -> rational

Returns the modified julian day for the TIME object.

Time Arithmetic

make-duration

[procedure] (make-duration [#:days 0] [#:hours 0] [#:minutes 0] [#:seconds 0] [#:milliseconds 0] [#:microseconds 0] [#:nanoseconds 0]) -> time

Returns a time-object of clock-type time-duration where the seconds and nanoseconds values are calculated by summing the keyword arguments.

one-second-duration

[procedure] (one-second-duration) -> time

one-nanosecond-duration

[procedure] (one-nanosecond-duration) -> time

zero-time

[procedure] (zero-time [TIME-TYPE time-duration]) -> time

TIME-FINE-GRAIN

Most minimum positive amount of time, as a duration.

divide-duration

[procedure] (divide-duration DURATION NUMBER) -> time

Returns a duration, from DURATION, divided by NUMBER, without remainder.

divide-duration!

[procedure] (divide-duration! DURATION NUMBER) -> time

Returns DURATION, divided by NUMBER, without remainder.

multiply-duration

[procedure] (multiply-duration DURATION NUMBER) -> time

Returns a duration, from DURATION, multiplied by NUMBER, truncated.

multiply-duration!

[procedure] (multiply-duration! DURATION NUMBER) -> time

Returns DURATION, multiplied by NUMBER, truncated.

time-negative?

[procedure] (time-negative? TIME) -> boolean

Is TIME negative?

A time object will never have a negative nanoseconds value.

time-positve?

[procedure] (time-positve? TIME) -> boolean

Is TIME positive?

time-zero?

[procedure] (time-zero? TIME) -> boolean

Is TIME zero?

time-abs

[procedure] (time-abs TIME) -> time

Returns the absolute time value, from TIME.

time-abs!

[procedure] (time-abs! TIME) -> time

Returns the absolute TIME value.

time-negate

[procedure] (time-negate TIME) -> time

Returns the sign inverted time value, from TIME.

time-negate!

[procedure] (time-negate! TIME) -> time

Returns the TIME sign inverted value.

Time Comparison

time-compare

[procedure] (time-compare TIME1 TIME2) -> integer

Returns -1, 0, or 1.

time-max

[procedure] (time-max TIME1 [TIME2...]) -> time

Returns the maximum time object from TIME1 TIME2....

time-min

[procedure] (time-min TIME1 [TIME2...]) -> time

Returns the minimum time object from TIME1 TIME2....

Dates

default-date-clock-type

[parameter] (default-date-clock-type [CLOCK-TYPE time-utc]) -> symbol

Sets or gets the clock-type used by default for conversion of a date to a time.

copy-date

[procedure] (copy-date DATE) -> date

Returns an exact copy of the specified DATE object.

date->seconds

[procedure] (date->seconds DATE [CLOCK-TYPE (default-date-clock-type)]) -> number

Returns the specified DATE as as an inexact seconds value, based on the CLOCK-TYPE.

The seconds value is relative to the TAI-EPOCH - 1 January 1970 CE at 00:00:00 UTC.

date->time

[procedure] (date->time DATE [CLOCK-TYPE (default-date-clock-type)]) -> time

Returns the specified DATE as a time-object of type CLOCK-TYPE.

date-zone-name

[procedure] (date-zone-name DATE) -> (or boolean string)

Returns the timezone abbreviation of the specified DATE object. The result is either a string or #f.

date-dst?

[procedure] (date-dst? DATE) -> boolean

Returns the daylight saving time flag of the specified DATE object.

Only valid for "current" dates. Historical dates will not have a correct setting. Future dates cannot have a correct setting.

Date Arithmetic

date-difference

[procedure] (date-difference DATE1 DATE2 [CLOCK-TYPE]) -> time

Returns the time-duration between DATE1 and DATE2.

date-add-duration

[procedure] (date-add-duration DATE DURATION [CLOCK-TYPE]) -> date

Returns a new date, the DATE plus the DURATION.

date-subtract-duration

[procedure] (date-subtract-duration DATE DURATION [CLOCK-TYPE]) -> date

Returns a new date, the DATE minus the DURATION.

date-adjust

[procedure] (date-adjust DATE AMOUNT DATE-KEY [CLOCK-TYPE]) -> date

Returns a new date, the DATE adjusted by the AMOUNT of DATE-KEY.

AMOUNT is an integer.

DATE-KEY is either 'years, 'quarters, 'months, 'days, 'hours, 'minutes, 'seconds, 'milliseconds, 'microseconds, or 'nanoseconds.

If the day of the month of DATE is greater than the number of days in the final month, the day of the month will change to the last day in the final month.

Adjusting a time DATE-KEY (ex: 'hours) follows the semantics of date-add-duration.

Date Comparison

date-compare

[procedure] (date-compare DATE1 DATE2) -> integer

Returns -1, 0, or 1.

date=?

[procedure] (date=? DATE1 DATE2) -> boolean

Is DATE1 on DATE2?

date>?

[procedure] (date>? DATE1 DATE2) -> boolean

Is DATE1 after DATE2?

date<?

[procedure] (date<? DATE1 DATE2) -> boolean

Is DATE1 before DATE2?

date>=?

[procedure] (date>=? DATE1 DATE2) -> boolean

Is DATE1 after or on DATE2?

date<=?

[procedure] (date<=? DATE1 DATE2) -> boolean

Is DATE1 before or on DATE2?

Timezone

Note that the daylight saving time (summer time) flag is always taken from the system, unless supplied. Any summer time rule component of a timezone-components object is not processed.

Remember that SRFI-19 timezone offset follows ISO 8601.

local-timezone-locale

[parameter] (local-timezone-locale [TZ-COMPONENTS])

Gets or sets the local timezone-locale object.

utc-timezone-locale

[parameter] (utc-timezone-locale [TZ-COMPONENTS])

Gets or sets the utc timezone-locale object.

Probably not a good idea to change the value.

timezone-locale-name

[procedure] (timezone-locale-name [TZ-COMPONENTS]) -> symbol

Returns the timezone-locale name of the supplied TZ-COMPONENTS, or the (local-timezone-locale) if missing.

timezone-locale-offset

[procedure] (timezone-locale-offset [TZ-COMPONENTS]) -> integer

Returns the timezone-locale offset of the supplied TZ-COMPONENTS, or the (local-timezone-locale) if missing.

timezone-locale-dst?

[procedure] (timezone-locale-dst? [TZ-COMPONENTS]) -> boolean

Returns the timezone-locale daylight saving time flag of the supplied TZ-COMPONENTS, or the (local-timezone-locale) if missing.

Input/Output Procedures

(require-extension srfi-19-io)

DATE->STRING conversion specifiers

The SRFI-19 document does not mention the padding character override feature for the normally zero-padded conversions f, H, I, j, m, M, N, S, y. If the tilde is followed by a - then padding is suppressed. If followed by a _ the space character is used for padding. Otherwise zero-padding is perfomed, the default.

~[-_][fHIjmMNSy]

format-date

[procedure] (format-date DESTINATION DATE-FORMAT-STRING DATE)

Displays a text form of the DATE on the DESTINATION using the DATE-FORMAT-STRING.

When the DESTINATION is #t the (current-output-port) is used, and the date object must be specified.

When the DESTINATION is a port it must be an output-port, and the date object must be specified.

When the DESTINATION is a number the (current-error-port) is the DESTINATION, and the DATE object must be specified.

When the DESTINATION is #f the result is returned as a string, and the DATE object must be specified.

[procedure] (format-date DATE-FORMAT-STRING DATE) -> {{string}}

Result is returned as a string.

scan-date

[procedure] (scan-date SOURCE TEMPLATE-STRING)

Reads a text form of a date from the SOURCE, following the TEMPLATE-STRING, and returns a date object.

When the SOURCE is #t the (current-input-port) is used.

When the SOURCE is a port it must be an input-port.

When the SOURCE is string it should be a date text form.

Time Period

Usage

(require-extension srfi-19-period)

A time-period is an interval, [begin end), where begin and end are time objects of the same clock type.

make-time-period

[procedure] (make-time-period BEGIN END [CLOCK-TYPE (default-date-clock-type)]) -> time-period

Returns a new time-period object. The clock types must be compatible.

BEGIN maybe a seconds value, a date, or a time (except time-duration). A seconds value or date are converted to CLOCK-TYPE.

END maybe a seconds value, a date, or a time. A seconds value or date are converted to the same clock type as BEGIN. A time-duration is treated as an offset from BEGIN.

copy-time-period

[procedure] (copy-time-period TIME-PERIOD) -> time-period

Returns a copy of TIME-PERIOD.

time-period-begin

[procedure] (time-period-begin TIME-PERIOD)

Returns the start time for the TIME-PERIOD.

time-period-end

[procedure] (time-period-end TIME-PERIOD) -> time

Returns the end time for the TIME-PERIOD.

time-period-last

[procedure] (time-period-last TIME-PERIOD) -> time

Returns the last time for the TIME-PERIOD; (time-period-end - TIME-FINE-GRAIN).

time-period-type

[procedure] (time-period-type TIME-PERIOD) -> symbol

Returns the clock-type of the TIME-PERIOD.

time-period?

[procedure] (time-period? OBJECT) -> boolean

Is OBJECT a time-period?

time-period-length

[procedure] (time-period-length TIME-PERIOD) -> time

Returns the time-duration of the TIME-PERIOD.

time-period-compare

[procedure] (time-period-compare TIME-PERIOD-1 TIME-PERIOD-2) -> integer

Returns -1 when TIME-PERIOD-1 < TIME-PERIOD-2, 0 when TIME-PERIOD-1 = TIME-PERIOD-2 and 1 TIME-PERIOD-1 > TIME-PERIOD-2.

time-period=?

[procedure] (time-period=? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Does TIME-PERIOD-1 begin & end with TIME-PERIOD-2?

time-period<?

[procedure] (time-period<? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Does TIME-PERIOD-1 end before TIME-PERIOD-2 begins?

time-period>?

[procedure] (time-period>? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Does TIME-PERIOD-1 begin after TIME-PERIOD-2 ends?

time-period<=?

[procedure] (time-period<=? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Does TIME-PERIOD-1 end on or before TIME-PERIOD-2 begins?

time-period>=?

[procedure] (time-period>=? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Does TIME-PERIOD-1 begin on or after TIME-PERIOD-2 ends?

time-period-preceding

[procedure] (time-period-preceding TIME-PERIOD-1 TIME-PERIOD-2) -> (or boolean time-period)

Return the portion of TIME-PERIOD-1 before TIME-PERIOD-2 or #f when it doesn't precede.

time-period-succeeding

[procedure] (time-period-succeeding TIME-PERIOD-1 TIME-PERIOD-2) -> (or boolean time-period)

Return the portion of TIME-PERIOD-1 after TIME-PERIOD-2 or #f when it doesn't succeed.

time-period-contains/period?

[procedure] (time-period-contains/period? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Is TIME-PERIOD-2 within TIME-PERIOD-1?

time-period-contains/time?

[procedure] (time-period-contains/time? TIME-PERIOD TIME) -> boolean

Is TIME within TIME-PERIOD?

TIME is converted to a compatible clock-type if possible.

time-period-contains/date?

[procedure] (time-period-contains/date? TIME-PERIOD DATE) -> boolean

Is DATE within TIME-PERIOD?

DATE is converted to a compatible time if possible.

time-period-contains?

[procedure] (time-period-contains? TIME-PERIOD OBJECT) -> boolean

Is OBJECT within TIME-PERIOD?

OBJECT maybe a time, date, or time-period.

time-period-intersects?

[procedure] (time-period-intersects? TIME-PERIOD-1 TIME-PERIOD-2) -> boolean

Does TIME-PERIOD-2 overlap TIME-PERIOD-1?

time-period-intersection

[procedure] (time-period-intersection TIME-PERIOD-1 TIME-PERIOD-2) -> (or boolean time-period)

The overlapping time-period of TIME-PERIOD-2 and TIME-PERIOD-1, or #f when no overlap.

time-period-union

[procedure] (time-period-union TIME-PERIOD-1 TIME-PERIOD-2) -> (or boolean time-period)

Returns the time-period spanned by TIME-PERIOD-1 and TIME-PERIOD-2, or #f when they do not intersect.

time-period-span

[procedure] (time-period-span TIME-PERIOD-1 TIME-PERIOD-2) -> time-period

Returns the time-period spanned by TIME-PERIOD-1 and TIME-PERIOD-2, including any gaps.

time-period-shift

[procedure] (time-period-shift TIME-PERIOD DURATION) -> time-period

Returns a copy of TIME-PERIOD shifted by DURATION.

time-period-shift!

[procedure] (time-period-shift! TIME-PERIOD DURATION) -> time-period

Returns TIME-PERIOD shifted by DURATION.

Usage

This module exports the time, date, timezone, and io APIs.

(require-extension srfi-19)

Examples

Prevent default timezone initialization by explicitly setting the 'timezone.

;must be done before 1st invocation of a srfi-19 export
(use locale)
(set-locale-category! 'timezone
  (posix-timezone-string->timezone-components
    ;some acceptable posix tz form
    "XSX+2:00XDX+1:00:00"
    ;source of tz info
    '("POSIX" "TZ")))

;now we can use srfi-19 in our runtime tz
(use srfi-19 extras)
(format #t "Present Day: ~A~%Present Time: ~A~%: Hah, hah, hah.~%"
  (current-date) (current-time))

Notes

The string->date and scan-date procedures will not create an incomplete date. At a minimum the input must include day, month and year components; the time and timezone components default to 0 and the locale, respectively.
31 December 1 BCE + 1 day -> 1 January 1 CE. There is no year 0. Unlike the ISO 8601 convention do not subtract 1 when converting a year BCE to a SRFI-19 year, just negate the year.
The SRFI-18 current-time and time? bindings conflict with SRFI-19 bindings.
A SRFI-18 time object is not accepted except by the conversion procedures.
The expression (time=? (seconds->time (nanoseconds->seconds (time->nanoseconds <time-duration>))) <time-duration>) might be #f, due to the use of inexact arithmetic.
Be careful using the procedures that return some form of 'julian-day'. These are implemented using the full numeric tower and will return rational numbers. Performing arithmetic with such a result will require the "numbers" egg. See the file "srfi-19-test.scm" in this egg for an example. This will be a problem with code that assumes fixnum and/or flonum only numbers. Perhaps an intermediate file that wraps any 'julian-day' calls and coerces to an inexact number. Use the wrapped 'julian-day' call in the problematic code.

Bugs and Limitations

Local timezone information is not necessarily valid for historic dates and problematic for future dates. Daylight saving time is especially an issue. Conversion of a time or seconds value to a local date will use the current timezone offset value. The current offset will reflect the daylight saving time status. So target dates outside of the DST period will be converted incorrectly!
Will not read years less than 1 properly. The ISO 8601 year convention for years 1 BCE and before and years 10000 CE and after is not supported.
Cannot swap SRFI 29 bundle. Fixed at load time.
Using date-adjust for the same date-key MomentJS says:

If you are adding hours, minutes, seconds, or milliseconds, the assumption is that you want precision to the hour, and will result in a different hour.

var m = moment(new Date(2011, 2, 12, 5, 0, 0)); // the day before DST in the US
m.hours(); // 5
m.add(24, 'hours').hours(); // 6

but this implementation says 1 day = 24 hours, so same hour.

Requirements

locale srfi-29 miscmacros numbers check-errors record-variants

Author

Kon Lovett

Version history

3.7.0: Added date->seconds.
3.6.0: Delay locale initialization.
3.5.0: Document time-record-printer-format & date-record-printer-format.
3.4.3: Fix #1000(?).
3.4.2: .
3.4.1: fix nanosecond squared value in date
3.4.0: add TIME-FINE-GRAIN, generalize make-time, add date-adjust.
3.3.6: Update leap second table.
3.3.5
3.3.4: Fix for ticket #630.
3.3.3: Fix for weekday name indexing, ticket #966.
3.3.2: Fix for removed ##sys#double->number.
3.3.1: Fix for time-monotonic->julian-day return, ticket #829.
3.3.0: Uses compiled setup-helper-mod.
3.2.0: Removed null time-period.
3.1.2: Fix for flonum (current-milliseconds). Fix for date-add/subtract-duration (actually time->date support for date-timezone-info). [Reported by Thomas Hintz]
3.1.1: Bug fix for non-unique month name key for May. Added padding character override information. The ZONE-OFFSET argument of make-date is optional. Added German bundle by Moritz Heidkamp.
3.1.0: Use of record-variants extension.
3.0.3: Bug fix for missing seconds->time & seconds->date in srfi-19. (Reported by Alex Suraci)
3.0.2: Bug fix for format-date output port check, format-date and scan-date argument type checks.
3.0.1: Bug fix for ~y input conversion.
3.0.0: Initial Chicken 4 release

License

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The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Scheme Request For Implementation process or editors, except as needed for the purpose of developing SRFIs in which case the procedures for copyrights defined in the SRFI process must be followed, or as required to translate it into languages other than English.

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