27 SRFI19 time utilities

(require (planet untyped/unlib/time))

Utility procedures for use with SRFI 19 times and dates.

(copy-date   date            [ #:nanosecond nanosecond             #:second second             #:minute minute             #:hour hour             #:day day             #:month month             #:year year             #:zone-offset zone-offset])   →   srfi:date?

date : srfi:date?

nanosecond : (U integer #f) = #f

second : (U integer #f) = #f

minute : (U integer #f) = #f

hour : (U integer #f) = #f

day : (U integer #f) = #f

month : (U integer #f) = #f

year : (U integer #f) = #f

zone-offset : (U integer #f) = #f

Creates a copy of date, substituting non-#f arguments for the values of the relevant fields.

(time->date time) → srfi:date?

time : (U time-tai? time-utc?)

Converts time to a date.

(time-utc? item) → boolean?

item : any

Predicate that recognises SRFI-19 times of the time-utc type.

(time-tai? item) → boolean?

item : any

Predicate that recognises SRFI-19 times of the time-tai type.

(time-duration? item) → boolean?

item : any

Predicate that recognises SRFI-19 times of the time-duration type.

(leap-year? year) → boolean?

year : integer?

Returns #t if year is a leap year.

(days-in-month month [year]) → integer?

month : integer?

year : integer? = 2001

Returns the number of days in month in year. month is numbered from 1 to 12. year defaults to a non-leap year if omitted.

Examples:

> (days-in-month 2)

28

> (days-in-month 2 2000)

29

(date-valid? date) → boolean?

date : srfi:date?

Returns #t if date is a valid date (its hour, day, month and so on are all in the correct ranges).

(date-day-of-the-week date)

→ (U 'mon 'tue 'wed 'thu 'fri 'sat 'sun)

date : date?

Returns a symbol representing the day of the week on date.

(date-week-day? date) → boolean?

date : date?

Returns #t if date is a Monday, Tuesday, Wednesday or Friday.

(time->ago-string   then            [ now             #:format format-string])   →   string?

then : (U time-tai time-utc)

now : (U time-tai time-utc) = (current-time (time-type then))

format-string : string? = "~a ~a ago"

Given the time of an event the past (and, optionally, another argument representing the current time), returns a textual description of the time passed since the event. Raises exn:fail:unlib if now is before then. See seconds->ago-string for examples.

The optional format-string should have two wildcards in it: one for the number (1, 2, 59) and one for the unit (seconds, minutes, days). The format string is ignored if the result is "yesterday".

(seconds->ago-string   secs            [ now             #:format format-string])   →   string?

secs : integer?

now : integer? = (current-seconds)

format-string : string? = "~a ~a ago"

Like time->ago-string but then and now are integer values like those output by current-seconds.

Examples:

> (seconds->ago-string (- (current-seconds) 45))

"45 seconds ago"

> (seconds->ago-string (- (current-seconds) (* 30 60)))

"30 minutes ago"

> (seconds->ago-string (- (current-seconds) (* 20 60 60)))

"20 hours ago"

> (seconds->ago-string (- (current-seconds) (* 25 60 60)))

"yesterday"

> (seconds->ago-string (- (current-seconds) (* 50 60 60)))

"2 days ago"

(current-year) → integer?

Returns the current four digit year.

(current-time-zone-offset) → integer?

Returns the current local time-zone offset in seconds (taking into account DST when and where appropriate).