Joseph Ferano
d57eeb3265
A (Vec Value) where a Value may itself hold a (Vec Value) — the recursive dynamic value an EDN reader has to answer with when nobody hands it a target struct type — was refused five different ways, and every one of the five gave the same reason: the container runtime is type-erased, so it copies and releases slots bytewise and cannot reach inside a slot. A free would release the slots and leave every block they point at stranded. That reason is about teardown, and it does not hold for a region. free-all never releases an individual slot; it takes the whole arena, and every block the elements own is in it, because they came out of it. The refusals were over-broad, and what they were guarding was never ownership — ownership tracking is untouched here, moves are still moves, and Types.is_move_only is the same function it was. So the question moved rather than disappeared. It could not stay at the type, because can-free is a capability on an allocator value and with-allocator rebinds a dynamic variable: which tier a (vec-new) will meet is not a property of the place its type is written. What is decided at compile time is only whether to ask, which is a property of the element type; the answer is a run-time branch on the allocator, one per container and never per element, because the alternative is a walk at release and a walk at release is the registry of destructors the frame tier's reset exists to not have. It is emitted at every growth and not only at the construction, because ZII means a container can exist without ever passing through (vec-new) — a case field left out of a literal, a global that starts zeroed — and those adopt the context on their first push. free on such a container is refused rather than made quietly shallow. It cannot recurse, which is the whole premise, and releasing the outer block alone would be "I freed it" written over a program that stranded everything inside; this runtime refuses that collapse everywhere else. The message names free-all, which is reachable by construction. clone stays refused for a reason the region does not dissolve, and the old message had bundled the two failures under one sentence: what disqualifies clone is not that it copies a header — so do at and get, and they are fine, because they promise nothing — it is that clone allocates a new block and promises independence, and a bytewise copy hands back elements still pointing into the original's region. A struct or union field is admitted only where the field's container holds owning elements, because that container can only have been built against a region. A field holding a plain (Vec u8) stays refused: nothing would force that one into a region, and two copies of the aggregate would be two headers over one heap block. vec-in-struct.flan still pins that. The epoch already covered use after free-all, including the case this makes reachable — an inner header copied out of an arena-held element into a local still traps, because an Allocator is a pointer and a copied-by-value one would carry its own epoch. arena-value.flan builds the value by hand; arena-edn.flan reads a real document through the tokenizer, and its reader takes no allocator and names none, because spec-memory.md already puts the allocator in the calling convention. arena-region.flan is the branch itself: run 0 is the (Vec (Vec i32)) control that must not trap, and runs 1 and 2 are the two ways this dies.
What is in here, and what is still true
These are the documents that are written once and read occasionally: the reasons behind the code, the
reports from finished investigations, and the record of individual work sessions. The documents that are
edited every day stay at the repository root, because source comments cite them by bare filename from
dozens of places and a path that moves is a path that rots. So plan.org, NEXT.md, spec-memory.md
and spec-conditions.md are one directory up, and everything here points back at them.
A note on how to read the citations below: a document in this directory that says plan.org means the
one at the repository root. Nothing in docs/ is named for a file at the root, so there is no ambiguity,
and rewriting a hundred prose mentions into ../plan.org would have cost more in readability than it
bought in precision.
If you have thirty seconds
Read BUILT.md. It is by far the largest document here and it is the one that pays: it holds the
reason behind every part of the compiler that exists, from why nothing is ever dlclosed to why the
printer is a compile-time walk over a type rather than a runtime function. It is current, it is
maintained, and deleting it would mean deriving all of it again. If you want to know why a thing is the
shape it is, the answer is in here.
After that, ../NEXT.md at the root for what is actually in flight, and REFERENCES.md here for
where the evidence comes from — the reference clones on this machine, what each one answers, and the
standing rule that a claim in these notes was read out of a clone rather than recalled.
The current documents
| File | What it is |
|---|---|
BUILT.md |
Why the parts that exist are shaped the way they are. The longest and the most load-bearing document in the repository. Current. |
DISCUSS.md |
Open questions, raised and deliberately not answered. Nothing in it is a decision or a task; entries that have since been answered say so and point at where the answer landed. Current, though it is half archive by now. |
PORTING.md |
What the author's game, siam-farmer, needs from Flan that Flan does not have yet, measured against the code that exists rather than against a plan. It is the requirements document the language is actually steering by. Current. |
REFERENCES.md |
The reference clones under ~/Repositories, what each one is consulted for, and the specific files and lines already cited from them. Current. |
The reports
| File | What it is |
|---|---|
SPIKE-GENERICS.md |
Milestone 5's parametric polymorphism, run early and out of order as a spike. The spike succeeded and generics landed, so this is the report of finished work rather than a live plan — but its findings about where the cost falls are still the reason the implementation looks the way it does. Historical, findings still stand. |
overview.md |
The first brainstorm, from before the language had S-expressions. It says in its own first line that it is superseded and no longer accurate. Kept for history only; its table of what changed is the only part worth reading. Superseded. |
handoffs/
One report per work session, each written by whoever held the branch at the time. They are the
operational record: what was attempted, what was measured, what was decided without being able to ask,
and what was left open for the next lane. They are all historical the moment they are written — a handoff
describes a session that has ended — but they are cited by name from source comments and from NEXT.md,
because the reasoning behind a guard or a calling convention is often only written down once and this is
where it was written.
Six of them are the hand-written x86-64 backend, read in the order the work happened:
handoffs/HANDOFF-x86-rt.md set the remaining-items list that the four after it close, handoffs/HANDOFF-x86-redef.md
built the redefinition emitter, handoffs/HANDOFF-x86-aggregates.md took that across the struct boundary,
handoffs/HANDOFF-x86-guards.md settled the two guards nothing reaches, handoffs/HANDOFF-x86-debug.md added debug
information, and handoffs/HANDOFF-x86-cost.md measured what the backend costs and set the survey running on its
own so a refusal cannot sit unnoticed again.
The other six sessions are unrelated to each other. handoffs/HANDOFF-arith.md is why a divide by zero is a condition
rather than a SIGFPE. handoffs/HANDOFF-raylib-ports.md is the running record of the last two raylib example
ports, whose lasting findings were folded into PORTING.md, and handoffs/HANDOFF-cimport-ptr.md is the arm
cimport.ml's header check had been promising in a comment and not implementing — which is what those two ports
found, worked around and wrote up. handoffs/HANDOFF-devtest-noise.md is the linker
error dune test used to print on every run. handoffs/HANDOFF-emacs-flake.md is the test_emacs flake that
turned out to be SIGPIPE killing the daemon mid-reply, and it is worth reading for the two mechanisms it
rules out as much as for the one it found. handoffs/HANDOFF-tidy.md is this reorganisation.