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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

Moduletext-iso8601-0.1.1Haskell2010

Data.Time.FromText

The RFC3339 grammar is below

date-fullyear   = 4DIGIT
date-month      = 2DIGIT  ; 01-12
date-mday       = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on month/year
time-hour       = 2DIGIT  ; 00-23
time-minute     = 2DIGIT  ; 00-59
time-second     = 2DIGIT  ; 00-58, 00-59, 00-60 based on leap second rules
time-secfrac    = "." 1*DIGIT
time-numoffset  = ("+" / "-") time-hour ":" time-minute
time-offset     = "Z" / time-numoffset

partial-time    = time-hour ":" time-minute ":" time-second [time-secfrac]
full-date       = date-fullyear "-" date-month "-" date-mday
full-time       = partial-time time-offset

date-time       = full-date "T" full-time

The parsers are a bit more lenient:

  • We also accept space instead of T date-time separator. (Allowed by RFC3339, forbidden by ISO8601)

  • Seconds are optional (allowed by ISO8601)

  • numerical timezone offset can be just ("+" / "-") time-hour or without a colon: ("+" / "-") time-hour time-minute (allowed by ISO8601). However we require colons in between hours, minutes and seconds in the time (partial-time) production, and dashes in full-date production.

  • We allow over 4 digits in the year part (and that is a reason to require dashes).

  • We allow -00:00 time offset. (Allowed by RFC3339, forbidden by ISO8601)

  • We always allow time with 60 seconds, we don't consult any leap second database.

  • 10 values
valueparseDay :: Text -> Either String Day
#

Parse a date of the form [+-]YYYY-MM-DD.

The year must contain at least 4 digits, to avoid the Y2K problem: a two-digit year YY may mean YY, 19YY, or 20YY, and we make it an error to prevent the ambiguity. Years from 0000 to 0999 must thus be zero-padded. The year may have more than 4 digits.

valueparseLocalTime :: Text -> Either String LocalTime
#

Parse a date and time, of the form YYYY-MM-DD HH:MM[:SS[.SSS]]. The space may be replaced with a T. The number of seconds is optional and may be followed by a fractional component.

valueparseTimeZone :: Text -> Either String TimeZone
#

Parse a time zone.

The accepted formats are Z, +HH, +HHMM, or +HH:MM. (+ can be -).

Accepts -23:59..23:59 range, i.e. HH < 24 and MM < 59. (This is consistent with grammar, and with what Python, Clojure, joda-time do).

valueparseZonedTime :: Text -> Either String ZonedTime
#

Parse a date with time zone info. Acceptable formats:

YYYY-MM-DD HH:MMZ
YYYY-MM-DD HH:MM:SSZ
YYYY-MM-DD HH:MM:SS.SSSZ

The first space may instead be a T, and the second space is optional. The Z represents UTC. The Z may be replaced with a time zone offset of the form +0000 or -08:00, where the first two digits are hours, the : is optional and the second two digits (also optional) are minutes.