Monthly Downloads: 16
Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
Tags: Data     Database     Codec    
Latest version: v0.3.0.0

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ULID Implementation in Haskell

Lexicographically sortable, 128-bit identifier with 48-bit timestamp and 80 random bits. Canonically encoded as a 26 character string, as opposed to the 36 character UUID.

Original implementation and spec: github.com/alizain/ulid

 01an4z07by   79ka1307sr9x4mv3

|----------| |----------------|
 Timestamp       Randomness
  48 bits         80 bits

Universally Unique Lexicographically Sortable Identifier

UUID can be suboptimal for many uses-cases because:

  • It isn't the most character efficient way of encoding 128 bits of randomness
  • UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
  • UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
  • UUID v4 provides no other information than randomness, which can cause fragmentation in many data structures

Instead, herein is proposed ULID:

  • 128-bit compatibility with UUID
  • 1.21e+24 unique ULIDs per millisecond
  • Lexicographically sortable
  • Canonically encoded as a 26 character string, as opposed to the 36 character UUID
  • Uses Douglas Crockford's base 32 for better efficiency and readability (5 bits per character)
  • Case insensitive
  • No special characters (URL safe)


A simple usage example:

module Main where

import Data.ULID

main :: IO ()
main = do
  -- Derive a ULID using the current time and default random number generator
  ulid1 <- getULID
  print ulid1

  -- Derive a ULID using a specified time and default random number generator
  ulid2 <- getULIDTime 1469918176.385 -- POSIX Time, millisecond precision
  print ulid2

As per the spec, it is also possible to use a cryptographically-secure random number generator to contribute the randomness. However, the programmer must manage the generator on their own.


module Main where

import Data.ULID

import qualified Crypto.Random       as CR
import qualified Data.ULID.Random    as UR
import qualified Data.ULID.TimeStamp as TS

main :: IO ()
main = do
  -- This default instantiation may not be sufficiently secure.
  -- See the docs at
  -- hackage.haskell.org/package/crypto-api-0.13.2/docs/Crypto-Random.html
  g <- (CR.newGenIO :: IO CR.SystemRandom)

  -- Generate timestamp from current time
  t <- TS.getULIDTimeStamp

  let ulid3 = case UR.mkCryptoULIDRandom g of
          Left err        -> error $ show err
          -- use g2, …, to continue generating secure ULIDs
          Right (rnd, g2) -> ULID t rnd

  print ulid3

Test Suite

stack test


stack bench
Running 1 benchmarks...
Benchmark ulid-bench: RUNNING...
217,868 op/s generate
Benchmark ulid-bench: FINISH