simon/jolt
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

docs: RFC 0003 — phm is a HAMT, sorted colls a red-black tree

Browse source 
The transients RFC described phm as "bucket-based copy-on-write" and mused about
"if it ever becomes a HAMT" — it is one now (jolt-684u), and sorted maps/sets are
a red-black tree (jolt-0hbr). Update the deviation/future-work notes accordingly.
This commit is contained in:
Yogthos 2026-06-16 09:12:30 -04:00
parent ce8d3a924d
commit 69f5a39f85
1 changed files with 5 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

8
docs/rfc/0003-transients.md
View file

@ -53,7 +53,7 @@ are identical (O(n) total either way) with a better constant in the loop and a
worse constant at the two edges. The pattern transients exist for — batch worse constant at the two edges. The pattern transients exist for — batch
construction — is fully served. What is NOT served is transient-editing a construction — is fully served. What is NOT served is transient-editing a
*large* collection to change a few keys: that's O(n) in Jolt vs O(log n) in *large* collection to change a few keys: that's O(n) in Jolt vs O(log n) in
Clojure, because `transient` flattens the pvec trie / phm buckets into a Clojure, because `transient` flattens the pvec trie / phm HAMT into a
native array/table and `persistent!` rebuilds them. native array/table and `persistent!` rebuilds them.
**No thread-ownership check.** JVM Clojure ≥1.7 also dropped the owner-thread **No thread-ownership check.** JVM Clojure ≥1.7 also dropped the owner-thread
@ -110,7 +110,9 @@ tiers as ordinary migration batches.
- pvec is already a 32-way trie with structural sharing (pv.janet), so - pvec is already a 32-way trie with structural sharing (pv.janet), so
Clojure-style O(1) `transient`/`persistent!` via editable nodes is a real Clojure-style O(1) `transient`/`persistent!` via editable nodes is a real
option for vectors — an internal change behind the same surface, not a option for vectors — an internal change behind the same surface, not a
semantics change. phm is bucket-based copy-on-write; the same trick applies semantics change. phm is now a HAMT with structural sharing too (jolt-684u),
if it ever becomes a HAMT. and sorted maps/sets are a red-black tree (jolt-0hbr), so the same editable-
node trick is open for those as well — the transient surface here is still the
copy-to-native-table flatten.
- `transient?` (Jolt extension, useful in tests) stays; Clojure has no public - `transient?` (Jolt extension, useful in tests) stays; Clojure has no public
predicate, so it must not leak into portability-sensitive code. predicate, so it must not leak into portability-sensitive code.