This library implements a Universally Unique Lexicographically Sortable Identifier (ULID) generator.


Note that most backends provide time stamps with lower granularity than required (i.e. seconds but not milliseconds). Also note that, per spec, within the same millisecond, monotonic sort order is not guaranteed.

The generation of ULIDs uses the /dev/urandom random number generator when available. This includes macOS, Linux, *BSD, and other POSIX operating-systems. On Windows, a pseudo-random generator is used but randomized using the current wall time.

ULIDs can be generated as atoms, lists of characters, or lists of character codes.

See also the ids and uuid libraries.

API documentation

Open the ../../docs/library_index.html#ulid link in a web browser.


To load all entities in this library, load the loader.lgt file:

| ?- logtalk_load(ulid(loader)).


To test this library predicates, load the tester.lgt file:

| ?- logtalk_load(ulid(tester)).

Generating ULIDs

By default, ULIDs are generated as atoms. For example:

| ?- ulid::generate(ULID).

To generate a ULID using a list of characters representation, use instead the ulid/1 parametric object:

| ?- ulid(chars)::generate(ULID).
ULID = ['0','1','H','0','J','3','2','Y','V','5','V','S','P','K','5','P','4','5','G','G','0','9','8','8','M','2']

Similar to get a ULID using a list of character codes representation:

| ?- ulid(codes)::generate(ULID).
ULID = [48,49,72,48,74,51,52,66,54,48,55,57,54,49,67,82,70,65,67,51,67,67,86,82,48,66]

It’s also possible to generate ULIDs from a given timestamp, i.e. the number of milliseconds since the Unix epoch (00:00:00 UTC on January 1, 1970), using the generate/2 predicate. The timestamp must be an integer. For example, assuming a backend Prolog system providing a time_stamp/1 predicate returning the Unix epoch in milliseconds:

| ?- time_stamp(Milliseconds), ulid(atom)::generate(Seconds, ULID).
Seconds = 1684245175344, ULID = '01H0JDBQ1GAWJF35C44Y5S97DX'

You can also use timestamp discrete components using the generate/8 predicate. For example:

| ?- ulid(atom)::generate(2023, 5, 17, 16, 23, 38, 591, ULID).

To extract the timestamp from a given ULID, use the timestamp/2 and timestamp/8 predicates. For example:

| ?- ulid(atom)::timestamp('01H0JDBQ1GAWJF35C44Y5S97DX', Milliseconds).
Milliseconds = 1684245175344

| ?- ulid(atom)::timestamp('01H0N8CDAZK75C5H3BJSGS4VCQ', Year, Month, Day, Hours, Minutes, Seconds, Milliseconds).
Year = 2023, Month = 5, Day = 17, Hours = 16, Minutes = 23, Seconds = 38, Milliseconds = 591

Type-checking ULIDs

This library also defines a ulid(Representation) type for type-checking ULIDs. For example, with an atom containing invalid characters:

| ?- type::check(ulid(atom), '01BX5ZIKBKALTAV9OEVGEMMVRY').
uncaught exception: domain_error(ulid,'01BX5ZIKBKALTAV9OEVGEMMVRY')