hodatime

A full-featured date and time library for Haskell, inspired by Noda Time (and, in turn, Joda Time) and Erik Naggum's The Long, Painful History of Time.

hodatime draws a clear line between physical time — instants, durations and intervals on a single global timeline — and civil time — calendar dates, local times, and the calendar-and-zone rules that connect the two. The type you are holding always tells you exactly what you can and cannot do with it, so whole classes of date/time mistakes simply do not type-check.

Features

• Physical vs. civil time, kept distinct at the type level (Instant / Duration / Interval versus CalendarDate / LocalTime / CalendarDateTime).
• Multiple calendars — Gregorian, ISO, Julian, Coptic, Persian (astronomical Solar Hijri), Islamic (parameterised over the leap-year rule) and Hebrew — with lossless conversion between them.
• Operating-system time zones — the IANA/Olson database on Unix, the registry on Windows — with explicit resolution of skipped and ambiguous local times across DST transitions.
• A type-safe, composable pattern system that derives a parser and a formatter together from a single field definition.
• Locale-aware formatting driven by the host system's locale data.

Example

import Data.HodaTime.Calendar.Gregorian (calendarDate, Month(..))
import Data.HodaTime.CalendarDate (dayOfWeek, withCalendar, CalendarDate)
import Data.HodaTime.Pattern (format)
import Data.HodaTime.Pattern.CalendarDate (pR)
import qualified Data.HodaTime.Calendar.Julian as Julian

-- Dates are smart-constructed; a date that cannot exist is Nothing
valentines = calendarDate 14 February 2024     -- a valid date (Just ...)
notADate   = calendarDate 30 February 2024     -- Nothing

-- Read-only components are plain functions
valentinesDoW = dayOfWeek <$> valentines       -- Just Wednesday

-- Convert losslessly to another calendar (the target is chosen by the result type)
julianChristmas :: Maybe (CalendarDate Julian.Julian)
julianChristmas = withCalendar <$> calendarDate 25 December 2024   -- 12 December 2024 in the Julian calendar

-- Format with a pattern (pR is the ISO-8601 round-trip date pattern)
isoText = format pR <$> calendarDate 23 April 2024                 -- Just "2024-04-23"

Installing

cabal install hodatime

or add hodatime to the build-depends of your package.

Documentation

The full API documentation is on Hackage. Start with the Data.HodaTime module, which gives a guided tour of the core concepts.

Changelog

Release notes are published on the GitHub releases page.

License

BSD-3-Clause. See LICENSE.