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(SRFI-19): Rewrite, adding descriptions of all

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functions, and a bit of an introduction.
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@ -2361,156 +2361,557 @@ specified in the SRFI. Using it avoids the described problems.
@section SRFI-19 - Time/Date Library @section SRFI-19 - Time/Date Library
@cindex SRFI-19 @cindex SRFI-19
This is an implementation of SRFI-19: Time/Date Library This is an implementation of the SRFI-19 time/date library. The
functions and variables described here are provided by
It depends on SRFIs: 6 (@pxref{SRFI-6}), 8 (@pxref{SRFI-8}), @example
9 (@pxref{SRFI-9}). (use-modules (srfi srfi-19))
@end example
This section documents constants and procedure signatures.
@menu @menu
* SRFI-19 Constants:: * SRFI-19 Introduction::
* SRFI-19 Current time and clock resolution:: * SRFI-19 Time::
* SRFI-19 Time object and accessors:: * SRFI-19 Date::
* SRFI-19 Time comparison procedures:: * SRFI-19 Time/Date conversions::
* SRFI-19 Time arithmetic procedures:: * SRFI-19 Date to string::
* SRFI-19 Date object and accessors:: * SRFI-19 String to date::
* SRFI-19 Time/Date/Julian Day/Modified Julian Day converters::
* SRFI-19 Date to string/string to date converters::
@end menu @end menu
@node SRFI-19 Constants @node SRFI-19 Introduction
@subsection SRFI-19 Constants @subsection SRFI-19 Introduction
All these are bound to their symbol names: @cindex universal time
@cindex atomic time
@cindex UTC
@cindex TAI
This module implements time and date representations and calculations,
in various time systems, including universal time (UTC) and atomic
time (TAI).
@example For those not familiar with these time systems, TAI is based on a
time-duration fixed length second derived from oscillations of certain atoms. UTC
time-monotonic differs from TAI by an integral number of seconds, which is increased
time-process or decreased at announced times to keep UTC aligned to a mean solar
time-tai day (the orbit and rotation of the earth are not quite constant).
time-thread
time-utc
@end example
@node SRFI-19 Current time and clock resolution @cindex leap second
@subsection SRFI-19 Current time and clock resolution So far, only increases in the TAI
@tex
$\leftrightarrow$
@end tex
@ifnottex
<->
@end ifnottex
UTC difference have been needed. Such an increase is a ``leap
second'', an extra second of TAI introduced at the end of a UTC day.
When working entirely within UTC this is never seen, every day simply
has 86400 seconds. But when converting from TAI to a UTC date, an
extra 23:59:60 is present, where normally a day would end at 23:59:59.
Effectively the UTC second from 23:59:59 to 00:00:00 has taken two TAI
seconds.
@example @cindex system clock
(current-date . tz-offset) In the current implementation, the system clock is assumed to be UTC,
(current-julian-day) and a table of leap seconds in the code converts to TAI. See comments
(current-modified-julian-day) in @file{srfi-19.scm} for how to update this table.
(current-time . clock-type)
(time-resolution . clock-type)
@end example
@node SRFI-19 Time object and accessors @cindex julian day
@subsection SRFI-19 Time object and accessors @cindex modified julian day
Also, for those not familiar with the terminology, a @dfn{Julian Day}
is a real number which is a count of days and fraction of a day, in
UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
4713 B.C. And a @dfn{Modified Julian Day} is the same, but starting
from 1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC.
@example @c The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
(make-time type nanosecond second) @c noon, UTC), but this is incorrect. It looks like it might have
(time? obj) @c arisen from the code incorrectly treating years a multiple of 100
(time-type time) @c but not 400 prior to 1582 as leap years, where instead the Julian
(time-nanosecond time) @c calendar should be used so all multiples of 4 before 1582 are leap
(time-second time) @c years.
(set-time-type! time type)
(set-time-nanosecond! time nsec)
(set-time-second! time sec)
(copy-time time)
@end example
@node SRFI-19 Time comparison procedures
@subsection SRFI-19 Time comparison procedures
Args are all @code{time} values. @node SRFI-19 Time
@subsection SRFI-19 Time
@cindex time
@example A @dfn{time} object has type, seconds and nanoseconds fields
(time<=? t1 t2) representing a point in time starting from some epoch. This is an
(time<? t1 t2) arbitrary point in time, not just a time of day. Although times are
(time=? t1 t2) represented in nanoseconds, the actual resolution may be lower.
(time>=? t1 t2)
(time>? t1 t2)
@end example
@node SRFI-19 Time arithmetic procedures The following variables hold the possible time types. For instance
@subsection SRFI-19 Time arithmetic procedures @code{(current-time time-process)} would give the current CPU process
time.
The @code{foo!} variants modify in place. Time difference @defvar time-utc
is expressed in @code{time-duration} values. Universal Coordinated Time (UTC).
@cindex UTC
@end defvar
@example @defvar time-tai
(time-difference t1 t2) International Atomic Time (TAI).
(time-difference! t1 t2) @cindex TAI
(add-duration time duration) @end defvar
(add-duration! time duration)
(subtract-duration time duration)
(subtract-duration! time duration)
@end example
@node SRFI-19 Date object and accessors @defvar time-monotonic
@subsection SRFI-19 Date object and accessors Monotonic time, meaning a monotonically increasing time starting from
an unspecified epoch.
@example Note that in the current implementation @code{time-monotonic} is the
(make-date nsecs seconds minutes hours same as @code{time-tai}, and unfortunately is therefore affected by
date month year offset) adjustments to the system clock. Perhaps this will change in the
(date? obj) future.
(date-nanosecond date) @end defvar
(date-second date)
(date-minute date)
(date-hour date)
(date-day date)
(date-month date)
(date-year date)
(date-zone-offset date)
(date-year-day date)
(date-week-day date)
(date-week-number date day-of-week-starting-week)
@end example
@node SRFI-19 Time/Date/Julian Day/Modified Julian Day converters @defvar time-duration
@subsection SRFI-19 Time/Date/Julian Day/Modified Julian Day converters A duration, meaning simply a difference between two times.
@end defvar
@example @defvar time-process
(date->julian-day date) CPU time spent in the current process, starting from when the process
(date->modified-julian-day date) began.
(date->time-monotonic date) @cindex process time
(date->time-tai date) @end defvar
(date->time-utc date)
(julian-day->date jdn . tz-offset)
(julian-day->time-monotonic jdn)
(julian-day->time-tai jdn)
(julian-day->time-utc jdn)
(modified-julian-day->date jdn . tz-offset)
(modified-julian-day->time-monotonic jdn)
(modified-julian-day->time-tai jdn)
(modified-julian-day->time-utc jdn)
(time-monotonic->date time . tz-offset)
(time-monotonic->time-tai time-in)
(time-monotonic->time-tai! time-in)
(time-monotonic->time-utc time-in)
(time-monotonic->time-utc! time-in)
(time-tai->date time . tz-offset)
(time-tai->julian-day time)
(time-tai->modified-julian-day time)
(time-tai->time-monotonic time-in)
(time-tai->time-monotonic! time-in)
(time-tai->time-utc time-in)
(time-tai->time-utc! time-in)
(time-utc->date time . tz-offset)
(time-utc->julian-day time)
(time-utc->modified-julian-day time)
(time-utc->time-monotonic time-in)
(time-utc->time-monotonic! time-in)
(time-utc->time-tai time-in)
(time-utc->time-tai! time-in)
@end example
@node SRFI-19 Date to string/string to date converters @defvar time-thread
@subsection SRFI-19 Date to string/string to date converters CPU time spent in the current thread. Not currently implemented.
@cindex thread time
@end defvar
@sp 1
@defun time? obj
Return @code{#t} if @var{obj} is a time object, or @code{#f} if not.
@end defun
@defun make-time type nanoseconds seconds
Create a time object with the given @var{type}, @var{seconds} and
@var{nanoseconds}.
@end defun
@defun time-type time
@defunx time-nanosecond time
@defunx time-second time
@defunx set-time-type! time type
@defunx set-time-nanosecond! time nsec
@defunx set-time-second! time sec
Get or set the type, seconds or nanoseconds fields of a time object.
@code{set-time-type!} merely changes the field, it doesn't convert the
time value. For conversions, see @ref{SRFI-19 Time/Date conversions}.
@end defun
@defun copy-time time
Return a new time object, which is a copy of the given @var{time}.
@end defun
@defun current-time [type]
Return the current time of the given @var{type}. The default
@var{type} is @code{time-utc}.
Note that the name @code{current-time} conflicts with the Guile core
@code{current-time} function (@pxref{Time}). Applications wanting to
use both will need to use a different name for one of them.
@end defun
@defun time-resolution [type]
Return the resolution, in nanoseconds, of the given time @var{type}.
The default @var{type} is @code{time-utc}.
@end defun
@defun time<=? t1 t2
@defunx time<? t1 t2
@defunx time=? t1 t2
@defunx time>=? t1 t2
@defunx time>? t1 t2
Return @code{#t} or @code{#f} according to the respective relation
between time objects @var{t1} and @var{t2}. @var{t1} and @var{t2}
must be the same time type.
@end defun
@defun time-difference t1 t2
@defunx time-difference! t1 t2
Return a time object of type @code{time-duration} representing the
period between @var{t1} and @var{t2}. @var{t1} and @var{t2} must be
the same time type.
@code{time-difference} returns a new time object,
@code{time-difference!} may modify @var{t1} to form its return.
@end defun
@defun add-duration time duration
@defunx add-duration! time duration
@defunx subtract-duration time duration
@defunx subtract-duration! time duration
Return a time object which is @var{time} with the given @var{duration}
added or subtracted. @var{duration} must be a time object of type
@code{time-duration}.
@code{add-duration} and @code{subtract-duration} return a new time
object. @code{add-duration!} and @code{subtract-duration!} may modify
the given @var{time} to form their return.
@end defun
@node SRFI-19 Date
@subsection SRFI-19 Date
@cindex date
A @dfn{date} object represents a date in the Gregorian calendar and a
time of day on that date in some timezone.
The fields are year, month, day, hour, minute, second, nanoseconds and
timezone. A date object is immutable, its fields can be read but they
cannot be modified once the object is created.
@defun date? obj
Return @code{#t} if @var{obj} is a date object, or @code{#f} if not.
@end defun
@defun make-date nsecs seconds minutes hours date month year zone-offset
Create a new date object.
@c
@c FIXME: What can we say about the ranges of the values. The
@c current code looks it doesn't normalize, but expects then in their
@c usual range already.
@c
@end defun
@defun date-nanosecond date
Nanoseconds, 0 to 999999999.
@end defun
@defun date-second date
Seconds, 0 to 60. 0 to 59 is the usual range, 60 is for a leap second.
@end defun
@defun date-minute date
Minutes, 0 to 59.
@end defun
@defun date-hour date
Hour, 0 to 23.
@end defun
@defun date-day date
Day of the month, 1 to 31 (or less, according to the month).
@end defun
@defun date-month date
Month, 1 to 12.
@end defun
@defun date-year date
Year, eg.@: 2003.
@end defun
@defun date-zone-offset date
Time zone, an integer number of seconds east of Greenwich.
@end defun
@defun date-year-day date
Day of the year, starting from 1 for 1st January.
@end defun
@defun date-week-day date
Day of the week, starting from 0 for Sunday.
@end defun
@defun date-week-number date dstartw
Week of the year, ignoring a first partial week. @var{dstartw} is the
day of the week which is taken to start a week, 0 for Sunday, 1 for
Monday, etc.
@c
@c FIXME: The spec doesn't say whether numbering starts at 0 or 1.
@c The code looks like it's 0, if that's the correct intention.
@c
@end defun
@c The SRFI text doesn't actually give the default for tz-offset, but
@c the reference implementation has the local timezone and the
@c conversions functions all specify that, so it should be ok to
@c document it here.
@c
@defun current-date [tz-offset]
Return a date object representing the current date/time UTC.
@var{tz-offset} is seconds east of Greenwich, and defaults to the
local timezone.
@end defun
@defun current-julian-day
@cindex julian day
Return the current Julian Day.
@end defun
@defun current-modified-julian-day
@cindex modified julian day
Return the current Modified Julian Day.
@end defun
@node SRFI-19 Time/Date conversions
@subsection SRFI-19 Time/Date conversions
@defun date->julian-day date
@defunx date->modified-julian-day date
@defunx date->time-monotonic date
@defunx date->time-tai date
@defunx date->time-utc date
@end defun
@defun julian-day->date jdn [tz-offset]
@defunx julian-day->time-monotonic jdn
@defunx julian-day->time-tai jdn
@defunx julian-day->time-utc jdn
@end defun
@defun modified-julian-day->date jdn [tz-offset]
@defunx modified-julian-day->time-monotonic jdn
@defunx modified-julian-day->time-tai jdn
@defunx modified-julian-day->time-utc jdn
@end defun
@defun time-monotonic->date time [tz-offset]
@defunx time-monotonic->time-tai time
@defunx time-monotonic->time-tai! time
@defunx time-monotonic->time-utc time
@defunx time-monotonic->time-utc! time
@end defun
@defun time-tai->date time [tz-offset]
@defunx time-tai->julian-day time
@defunx time-tai->modified-julian-day time
@defunx time-tai->time-monotonic time
@defunx time-tai->time-monotonic! time
@defunx time-tai->time-utc time
@defunx time-tai->time-utc! time
@end defun
@defun time-utc->date time [tz-offset]
@defunx time-utc->julian-day time
@defunx time-utc->modified-julian-day time
@defunx time-utc->time-monotonic time
@defunx time-utc->time-monotonic! time
@defunx time-utc->time-tai time
@defunx time-utc->time-tai! time
@sp 1
Convert between dates, times and days of the respective types. For
instance @code{time-tai->time-utc} accepts a @var{time} object of type
@code{time-tai} and returns an object of type @code{time-utc}.
For conversions to dates, @var{tz-offset} is seconds east of
Greenwich. The default is the local timezone.
The @code{!} variants may modify their @var{time} argument to form
their return. The plain functions create a new object.
@end defun
@node SRFI-19 Date to string
@subsection SRFI-19 Date to string
@cindex date to string
@defun date->string date [format]
Convert a date to a string under the control of a format.
@var{format} should be a string containing @samp{~} escapes, which
will be expanded as per the following conversion table. The default
@var{format} is @samp{~c}, a locale-dependent date and time.
Many of these conversion characters are the same as POSIX
@code{strftime} (@pxref{Time}), but there are some extras and some
variations.
@multitable {MMMM} {MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM}
@item @nicode{~~} @tab literal ~
@item @nicode{~a} @tab locale abbreviated weekday, eg.@: @samp{Sun}
@item @nicode{~A} @tab locale full weekday, eg.@: @samp{Sunday}
@item @nicode{~b} @tab locale abbreviated month, eg.@: @samp{Jan}
@item @nicode{~B} @tab locale full month, eg.@: @samp{January}
@item @nicode{~c} @tab locale date and time, eg.@: @*
@samp{Fri Jul 14 20:28:42-0400 2000}
@item @nicode{~d} @tab day of month, zero padded, @samp{01} to @samp{31}
@c Spec says d/m/y, reference implementation says m/d/y.
@c Apparently the reference code was the intention, but would like to
@c see an errata published for the spec before contradicting it here.
@c
@c @item @nicode{~D} @tab date @nicode{~d/~m/~y}
@item @nicode{~e} @tab day of month, blank padded, @samp{ 1} to @samp{31}
@item @nicode{~f} @tab seconds and fractional seconds,
with locale decimal point, eg.@: @samp{5.2}
@item @nicode{~h} @tab same as @nicode{~b}
@item @nicode{~H} @tab hour, 24-hour clock, zero padded, @samp{00} to @samp{23}
@item @nicode{~I} @tab hour, 12-hour clock, zero padded, @samp{01} to @samp{12}
@item @nicode{~j} @tab day of year, zero padded, @samp{001} to @samp{366}
@item @nicode{~k} @tab hour, 24-hour clock, blank padded, @samp{ 0} to @samp{23}
@item @nicode{~l} @tab hour, 12-hour clock, blank padded, @samp{ 1} to @samp{12}
@item @nicode{~m} @tab month, zero padded, @samp{01} to @samp{12}
@item @nicode{~M} @tab minute, zero padded, @samp{00} to @samp{59}
@item @nicode{~n} @tab newline
@item @nicode{~N} @tab nanosecond, zero padded, @samp{000000000} to @samp{999999999}
@item @nicode{~p} @tab locale AM or PM
@item @nicode{~r} @tab time, 12 hour clock, @samp{~I:~M:~S ~p}
@item @nicode{~s} @tab number of full seconds since ``the epoch'' in UTC
@item @nicode{~S} @tab second, zero padded @samp{00} to @samp{60} @*
(usual limit is 59, 60 is a leap second)
@item @nicode{~t} @tab horizontal tab character
@item @nicode{~T} @tab time, 24 hour clock, @samp{~H:~M:~S}
@item @nicode{~U} @tab week of year, Sunday first day of week,
@samp{00} to @samp{52}
@item @nicode{~V} @tab week of year, Monday first day of week,
@samp{01} to @samp{53}
@item @nicode{~w} @tab day of week, 0 for Sunday, @samp{0} to @samp{6}
@item @nicode{~W} @tab week of year, Monday first day of week,
@samp{00} to @samp{52}
@c The spec has ~x as an apparent duplicate of ~W, and ~X as a locale
@c date. The reference code has ~x as the locale date and ~X as a
@c locale time. The rule is apparently that the code should be
@c believed, but would like to see an errata for the spec before
@c contradicting it here.
@c
@c @item @nicode{~x} @tab week of year, Monday as first day of week,
@c @samp{00} to @samp{53}
@c @item @nicode{~X} @tab locale date, eg.@: @samp{07/31/00}
@item @nicode{~y} @tab year, two digits, @samp{00} to @samp{99}
@item @nicode{~Y} @tab year, full, eg.@: @samp{2003}
@item @nicode{~z} @tab time zone, RFC-822 style
@item @nicode{~Z} @tab time zone symbol (not currently implemented)
@item @nicode{~1} @tab ISO-8601 date, @samp{~Y-~m-~d}
@item @nicode{~2} @tab ISO-8601 time+zone, @samp{~k:~M:~S~z}
@item @nicode{~3} @tab ISO-8601 time, @samp{~k:~M:~S}
@item @nicode{~4} @tab ISO-8601 date/time+zone, @samp{~Y-~m-~dT~k:~M:~S~z}
@item @nicode{~5} @tab ISO-8601 date/time, @samp{~Y-~m-~dT~k:~M:~S}
@end multitable
@end defun
Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently
described here, since the specification and reference implementation
differ.
Currently Guile doesn't implement any localizations for the above, all
outputs are in English, and the @samp{~c} conversion is POSIX
@code{ctime} style @samp{~a ~b ~d ~H:~M:~S~z ~Y}. This may change in
the future.
@node SRFI-19 String to date
@subsection SRFI-19 String to date
@cindex string to date
@c FIXME: Can we say what happens when an incomplete date is
@c converted? Ie. fields left as 0, or what? The spec seems to be
@c silent on this.
@defun string->date input template
Convert an @var{input} string to a date under the control of a
@var{template} string. Return a newly created date object.
Literal characters in @var{template} must match characters in
@var{input} and @samp{~} escapes must match the input forms described
in the table below. ``Skip to'' means characters up to one of the
given type are ignored, or ``no skip'' for no skipping. ``Read'' is
what's then read, and ``Set'' is the field affected in the date
object.
For example @samp{~Y} skips input characters until a digit is reached,
at which point it expects a year and stores that to the year field of
the date.
@multitable {MMMM} {@nicode{char-alphabetic?}} {MMMMMMMMMMMMMMMMMMMMMMMMM} {@nicode{date-zone-offset}}
@item
@tab Skip to
@tab Read
@tab Set
@item @nicode{~~}
@tab no skip
@tab literal ~
@tab nothing
@item @nicode{~a}
@tab @nicode{char-alphabetic?}
@tab locale abbreviated weekday name
@tab nothing
@item @nicode{~A}
@tab @nicode{char-alphabetic?}
@tab locale full weekday name
@tab nothing
@c Note that the SRFI spec says that ~b and ~B don't set anything,
@c but that looks like a mistake. The reference implementation sets
@c the month field, which seems sensible and is what we describe
@c here.
@item @nicode{~b}
@tab @nicode{char-alphabetic?}
@tab locale abbreviated month name
@tab @nicode{date-month}
@item @nicode{~B}
@tab @nicode{char-alphabetic?}
@tab locale full month name
@tab @nicode{date-month}
@item @nicode{~d}
@tab @nicode{char-numeric?}
@tab day of month
@tab @nicode{date-day}
@item @nicode{~e}
@tab no skip
@tab day of month, blank padded
@tab @nicode{date-day}
@item @nicode{~h}
@tab same as @samp{~b}
@item @nicode{~H}
@tab @nicode{char-numeric?}
@tab hour
@tab @nicode{date-hour}
@item @nicode{~k}
@tab no skip
@tab hour, blank padded
@tab @nicode{date-hour}
@item @nicode{~m}
@tab @nicode{char-numeric?}
@tab month
@tab @nicode{date-month}
@item @nicode{~M}
@tab @nicode{char-numeric?}
@tab minute
@tab @nicode{date-minute}
@item @nicode{~S}
@tab @nicode{char-numeric?}
@tab second
@tab @nicode{date-second}
@item @nicode{~y}
@tab no skip
@tab 2-digit year
@tab @nicode{date-year} within 50 years
@item @nicode{~Y}
@tab @nicode{char-numeric?}
@tab year
@tab @nicode{date-year}
@item @nicode{~z}
@tab no skip
@tab time zone
@tab date-zone-offset
@end multitable
Notice that the weekday matching forms don't affect the date object
returned, instead the weekday will be derived from the day, month and
year.
Currently Guile doesn't implement any localizations for the above,
month and weekday names are always expected in English. This may
change in the future.
@end defun
@example
(date->string date . format-string)
(string->date input-string template-string)
@end example
@c srfi-modules.texi ends here @c srfi-modules.texi ends here