This is an implementation of ULID in portable R7RS Scheme.

Requires the following libraries:

• (scheme base)
• (scheme bitwise)
• (scheme comparator)
• (scheme vector)
• (srfi 13) (string)
• (srfi 19) (time & date)
• (srfi 27) (random numbers)
• (srfi 145) (assumptions)
• (srfi 227) (optional arguments) - Optional

(define gen-ulid (make-ulid-generator))

Creates a new ULID generator. You can pass a random source (srfi-27) to make-ulid-generator to use your random source; if no randon source is passed, default-random-source is used.

(gen-ulid)  ;⇒ #<ulid>

Calling the generator procedure created with make-ulid-generator returns a new ULID object. You can retrieve its timestamp and randomness fields by ulid-timestamp and ulid-randomness, both in exact nonnegative integers, respectively.

Note: According to ULID spec, if more than one ULID is generated within the same millisecond timestamp, the subsequent ULIDs gets randomness field incremented from the previous one. There's a extremely small chance that the randomness field overflows, in such case ULID spec says the generation fails. Our implementation wait for the next millisecond timestamp instead. Theoretically this will be an issue if the caller wants to generate close to 2^80 ULIDs per milliseconds constantly; in reality it's very unlikely.

The ULID generator can take an optional timestamp argument; it is useful when importing existing data keeping timestamp part.

(define u (gen-ulid))
(ulid->string u)   ;⇒ "01FV9V6CVKT28VPQ12NTFFDSZ1"
(ulid->bytevector u) ;⇒ #u8(1 126 211 179 51 115 208 145 187 92 34 174 158 246 231 225)
(ulid->integer u)  ;⇒ 1987751186151511620525844062631552993

Convert ULID to a string, a bytevector, or an exact integer, respectively.

(string->ulid "01FV9V6CVKT28VPQ12NTFFDSZ1")
  ;⇒ #<ulid>
(bytevector->ulid '#u8(1 126 211 179 51 115 208 145 187 92 34 174 158 246 231 225))
  ;⇒ #<ulid>
(integer->ulid 1987751186151511620525844062631552993)
  ;⇒ #<ulid>

Convert a string, a bytevector, or an exact integer to ULID, respectively.

(ulid=? ulid1 ulid2)
(ulid<? ulid1 ulid2)
(ulid-hash ulid)

Equality predicate, ordering predicate, and hash function.

ulid-comparator

A comparator suitable for ULID.

Run tests/ulid.scm. For Gauche, you can run tests/gauche.scm.

Copy ulid.sld and ulid-impl.scm to wherever your load-path can see.

There're a couple of cond-expand in ulid-impl.scm that an implementation may have better ways than the portable code. Feel free to add your implementation-specific support and send me PR.