Closing the window of a printing program left the pipe full, and the flushes
on the way out blocked on a compiler thread that was busy answering the very
request asking to run it again. program_state still said RUNNING, so rerun
refused a finished program as "the program is already running".
Two flushes moved. flan_exit no longer flushes before the hook -- exit(3)
flushes for itself, so that call only ever ran on the merged path, and there
it was the first thing to block. flan_merged_park flips the state under the
lock first and flushes after, because a state flip is two stores and cannot
wait on anything.
What widens is the window in which the program is parked and not yet on the
condvar. Nothing is lost there: program_asked is the fact and a signal
delivered to nobody is discarded. Two re-runs in that window are both
answered ok for one run, which is the trade against a refusal that was false.
The merged build's stdout is a 64K pipe back into the daemon's own process,
and the accept loop is the only thing reading it -- which it is not doing
while serve is answering a request. The two five-second waits for a frame
boundary now drain the pipe on every tick, so a program stopped inside fwrite
is one the daemon lets go rather than one it waits out and then accuses of
not calling agent/poll.
drain and not take: the text stays in the buffer until with_output puts it on
the reply, which is where the output an evaluation caused belongs. And the
drain sits beside the sleep rather than inside the select, because a readable
pipe would make the tick free and count the timeout out in a fraction of it.
dev-chatty.flan prints 4K a frame, which is the only fixture here that fills
the pipe at all; without the drain it fails in 5.1s with the old sentence.
The arm was written with the others and through the same deferral, and neither
the generics row in test_flan.ml nor the paragraph in BUILT.md that enumerates
what defers had it. Its placeholder is get's, for get's reason: it answers an
(Option V), so the match around it still has to check while the key is a
variable.
FIX.org carried Addr(Pfield ...) on an Option as a hole in both backends. It is
not reachable from the language: a field access goes through struct_target,
which admits a struct or a pointer to one and refuses everything else by name
with a location, so (addr (.x o)) is refused at the field and never reaches a
place. The node that failed was one the compiler built for itself.
The refusal is pinned on the bare field and on the address of one, and FIX.org
now records the finding, including the asymmetry that stays: the x86 backend
lays out an Option's tag and value as fields and the LLVM backend does not.
Neither path is reachable, so matching them would be untestable code written to
balance a road nobody drives on.
Every number-to-text conversion wrote into one file-static in the runtime and
answered a slice over it, and nothing copied. Two of them in one expression
printed the second number twice — no crash, no diagnostic, and nothing a
sanitizer could find, because every byte read was inside an object that was
alive. The wrong object.
The buffer is now the caller's, one frame slot per call site. The slot is
allocated in the checker rather than in either backend: a slot is a
function-lifetime location in both of them, where an x86 backend temporary is
bump-allocated and reclaimed at the end of the expression that made it — which
is the one lifetime a returned slice must outlive. Each backend gains one
pointer argument and no reasoning of its own, which is what keeps them
symmetric.
The static is gone rather than left unused, since a buffer with nothing but a
comment beside it is a loaded gun. What remains is the ordinary lifetime a
pointer into a frame has: storing one of these slices in a container that
outlives the frame, or returning it, is still a copy the caller has to make.
NEXT.md's sharp edge now says that instead of what it used to say.
The writer is the game thread, in every allocation and every free; the reader
is the agent's listener, on a program that is running. Nothing stood between
them. The consequence is not a slightly wrong count: a row's type pointer and
its length mean nothing apart, and a reader that takes the new pointer with the
old length reads off the end of a string literal.
Each entry now carries the watch table's seqlock, odd while it is written, and
a reader copies the entry and re-reads the counter before believing it. The
compaction bumps a table-wide counter around itself, because it moves entries
between slots and no per-slot counter can describe that; a scan that sees that
counter move walks again. It clears the table slot by slot rather than with one
memset, since the memset would zero the counters a reader was holding.
The breakdown and the leak report stay answerable while the program runs, which
is the moment they are for. reg at does not: whether one address is still live
is exactly what a running program is changing, so it is refused the way every
break verb is refused, which is what the daemon already did on its own side.
(map-remove! m k) answers the value that was there, or None, which is the
answer get already gives and for the same reason: a key that is not in the map
is an answer, not a failure. Handing the value back rather than dropping it
makes "take this out and use it" one call instead of two that hash the key
twice.
The removal shifts the probe run back over the hole. A Robin Hood lookup stops
at the first empty slot, so a hole left in the middle of a run hides every
entry after it — and the hidden ones are precisely what a test that only asks
after what it removed never looks at, which is why the program removes a
thousand of two thousand keys and then asks for the other thousand.
Odin was read rather than recalled here, and it does the opposite: its erase
marks a tombstone and its insert carries the repair loop. Staying tombstone-
free keeps the shape the rest of the file already assumed, and the lookups —
which outnumber the removals — pay nothing for it. The note in the runtime and
the two in BUILT.md that said Odin deletes by backward shift were describing
Odin's insert, and now say which is which.
It allocates nothing and releases nothing, so there is no guard around it and
it means the same thing on a map in an arena as on one in the heap: a key and a
value live inside the one block the map allocated, and there was never anything
per entry to hand back.
The argument vector's malloc was unchecked, and a failure there would have
published a null pointer with a length beside it. It now dies naming what it
was building, because argv has no allocation site for a condition to hang on.
flan_slurp_into read a capacity of elements as a capacity of bytes and skipped
the epoch check every other container operation runs. The element size is now
a parameter and the length it publishes counts whole elements, so the day slurp
answers something other than (Vec u8) it does not answer with bytes nobody
wrote.
A string with a NUL in it is refused at the C boundary, which is the policy
flan_path_cstr has always had for a path: C reads to the first NUL, so what
crosses is a prefix of what was passed, and a window title is no different from
a filename in that respect. The refusal names the declare-c, which is the name
the program's author wrote.
The runtime's two translation units are compiled with -Wall -Wextra. They were
already clean under both; the flag is there so the next one is caught rather
than read.
The generation word keeps its place and loses its "yet": a reader for it is a
third word on every slice in the language, which is a spec amendment rather
than a runtime patch, and the comment now says so where someone deciding to
trust the word would read it.
--dev builds a program whose call sites go through indirection cells so
something can attach and redefine through them. Nothing can attach to a
process this command builds, execs, waits for and deletes, so the flag had no
meaning here -- and an --x86 --dev route through run would have falsified
Build's own statement that flan dev never reaches that fork because --x86 is
read only by flan build. It falls into the refusal arm with a sentence
instead.
A GitHub Actions workflow on push: dune build, dune test --force, dune build
@checks. @x86 parity is not under dune test, so the routine suite never
protected it; both of this repository's silent failures would have been caught
by one person typing one command, and the problem was never the command.
The suite step keeps its log and greps it for Fatal error, because a suite
that passes while leaving an unhandled exception on stderr is one that is
telling you something and being ignored.
FLAN_LLC is pinned to the llc matching clang's version rather than left to
PATH order: the live loop goes llc + ld -shared + dlopen and never calls the
clang driver, so a mismatch breaks every reload test while flan build keeps
working, which is a bad failure to debug from a log.
What an Ubuntu runner cannot cover -- raylib by exact Fedora soname,
emscripten, a wasi sysroot, lldb -- is written in the workflow with the skip
path each one already takes, so the tick does not read as more than it is.
README.md and test/dune both said there was no CI; both now say what there is
and what it misses.
The tagged sum is Tast.data now and Tast.unions is C's untagged union, which
arrives as a structure whose every field sits at offset zero. That is a
layout, and a layout is the one thing an object has none of here -- two
properties cannot share a run of bytes -- so it is refused with the type's own
name rather than met as "not a struct".
Two hardenings the sweep could not have found. $str built a view onto node's
Buffer pool, where small Buffers share one ArrayBuffer, so a write through one
string literal's slice could have reached another's bytes; native puts a
literal in .rodata where that write is a fault. And copy_of's Option arm named
its argument three times, which evaluates it three times.
SURVEY_FLAGS reaches both sides now, as it does in the x86 sweep, so the
unchecked indexing path -- a bare a[i] with no $at around it, which nothing
had ever run -- is swept too: 23 match, 0 differ.
web/examples/ffi.flan opened with (declare cos-f64 [x f64] f64 "cos"), which
was a fine one-liner until the prelude grew cos-f64 an hour ago. @page caught
it: "cos-f64 is defined twice", with the prelude line named as the other site.
It is cosh now. Same shape, same answer, and the collision is worth keeping in
the page rather than editing around silently -- a reader reaching for a libm
function needs to know the common ones are already there and that a second
declaration of a name is refused, not shadowed. The example says so in one
sentence.
This is the cost of filling out the prelude, and it is the whole of it: a
program that declared one of the new names for itself stops compiling, with
both sites named. Nothing in the corpus or in examples/ hit it; this page did.
The alias is @x86's shape and deps: one rule over spike/js/survey.sh, FLAN
passed so the script does not start a dune inside dune's own lock. It is not
in the default run and node is probed rather than assumed.
spike/js/survey.sh is the x86 sweep's shape with one deliberate difference in
what it counts. That backend is behind, so a refusal there is a regression and
its strict mode fails on one. This is a dialect, so a refusal is the design
working -- a pointer, an allocator, a Map, the FFI and conditions are refused
permanently and correctly. What fails the @js alias is a DIFFER, which is a
wrong answer, and a CRASH, which is JS this backend emitted and node would not
run.
Two probes carry the decisions the corpus does not reach. p1-int-semantics
prints wrapping at all eight widths, a multiply past 2^53, truncating division
with a negative operand, shifts whose count is out of range, bitwise over a
u32, f32 that is not a double, and the conversions both ways -- 35 lines, all
identical to the LLVM build. It found two real bugs: >>> binds tighter than &
in JavaScript, so a bit-and on a u32 answered -1; and a 64-bit value through
Number() rounds to 53 bits before it can be truncated, so (i32 i64hi) answered
0 where it must answer -1.
p2-value-copies goes past values.flan to the cases a shallow copy would pass:
a struct inside a struct, a struct returned out of a function, an element read
out of an array of structs, and a global.
Also fixed, and all three were found by the sweep rather than by reading: a
unit-typed call in statement position was compiled to an expression nobody
emitted, so (load-xs) silently did not happen; an arrow body that starts with
a brace is a block, so a zeroed array of structs was a syntax error; and a
bounds message must carry the index expression's location, not the form's,
because that is the one emit.ml passes to check_at.
Render reads an Option's tag as field 0 and a union's as field 0, which is the
LLVM layout and not this one, so both are answered here rather than refused.
fdefers is dropped rather than refused: nothing in the dialect can start a
transfer, so the transfer exit path is unreachable, and refusing it would have
refused every program that writes a plain defer.
lib/js.ml lowers the same checked Tast the other two backends take to one
CommonJS file, by object mapping rather than linear memory: docs/DISCUSS.md
item 5 settled that fork before this was written, and item 5's consequence is
the whole shape of the file. Object mapping means the host's collector owns
every value, so there is no (Ptr T), no free, no arena and no allocator, and a
program that uses one is refused by name with a location rather than compiled
badly.
flan build --target=js leaves Build.executable through its own two lines,
before anything that assumes a clang: there is no object to compile and no
linker to run. --dev, --debug, --sanitize and --x86 are refused there rather
than swallowed. Js.Unsupported exits 3 beside X86.Unsupported, so a sweep can
count refused-by-name apart from did-not-compile.
What runs end to end: integer and float arithmetic with the normalisation each
width needs, let, if, while with break and continue, calls, function values,
structs, fixed arrays, slices, unions, options, match, and println through the
same structural printer the other backends walk.
Value semantics is the trap the object mapping sets and the reason the header
carries a section on it. A Flan struct and a fixed array copy on assignment and
a JS object does not, so every site emit.ml memcpys emits a generated
Point$copy here. Fable's JS backend faces the same question for F# structs and
answers it the other way -- it inserts no clone, and its Rust backend does --
so the divergence is deliberate and the survey pins it.
Both corpora are explicit lists and not globs, so a program added to
test/programs is covered by dune test and by @x86 and by nothing else until
somebody types its name here. files.flan, math3.flan and time.flan are typed.
time.flan is the one with something to say. getenv hands back a slice viewing
the process environment and never a copy, which is the exact shape a
use-after-free or an off-by-one length would be, and neither ASan nor memcheck
had ever seen it. files.flan brings three more path buffers through
flan_path_cstr. math3.flan is the cheap one and is here for completeness.
files.flan makes and removes its own tree, so the sweeps' two runs of it see
the same directory both times.
@sanitize is clean with all three in. @valgrind is not run here -- it is tens
of minutes and opt-in -- so those three entries are checked by the next person
who runs the alias.
Five more: file-exists?, file-size, delete-file, rename-file and
make-directory. The interesting thing is not the list, it is the line drawn
through it.
file-exists? and file-size answer a value -- a bool and an (Option i64) -- and
are prelude functions over one declare that the compiler knows nothing about.
Absence is the reply to those two questions and not a fault, so a condition
would make the ordinary case pay for a handler search, and there is no restart
a handler could take that would turn "it is not there" into a different
answer.
delete-file, rename-file and make-directory answer () and signal FileError,
and they are check.ml builtins for the one thing a declare cannot do: they go
through file_guard, so each failure arrives under retry and use-value. Those
are restarts a handler really can take -- make the parent directory and retry,
or supply another path -- which is exactly the case a bool return throws away.
op continues the prelude's numbering as 2, 3 and 4.
One C function behind the two questions rather than two, because they are one
question: stat answers whether the path resolves and how big it is in the same
breath. It is stat and not flan_file_size's fopen-plus-ftell, which is shaped
by slurp being about to read the file and is wrong as a general size -- fopen
on a directory succeeds on Linux and ftell then answers a number that is not a
file size. The two coexist and answer different questions.
rename holds the source in the guard's path slot, so a use-value renames a
different file to the same destination. Both readings are plausible until
somebody says which, so check.ml says which.
The errno mapping is not extended. Its three buckets are what a handler can
act on; EEXIST and ENOTEMPTY land in io with everything else, and that is
honest until conditions have a hierarchy to hang a fourth reason off.
All three carry barf's decision 2 unchanged: they change the filesystem, so on
the web they signal rather than succeeding quietly into a filesystem the page
throws away.
Not here, and not half-parsed either: a directory listing, which needs an
allocating builtin and a Vec of owned strings, and streaming IO. Neither has
a name to trip over.
programs/files.flan makes and removes its own tree and takes both restarts on
operations that write. The runtime additions continue the block at the end of
flan_rt.c.
Nothing in it could. A game got a clock from raylib and a program without a
window had none at all, so "how long did that take" was unanswerable in the
half of daily use that is a tool rather than a game.
Two clocks, because the mistake a single one invites is using it for the other
job. monotonic-ns measures: it never goes backwards, nothing adjusts it, and
its zero is arbitrary, so it is meaningless alone and correct as a difference.
unix-ns dates: nanoseconds since 1970, which is what goes in a save file, and
which jumps in either direction when somebody sets the system clock. The names
are picked so that reaching for the wrong one reads wrong.
This is Odin's shape, from core/time/time.odin and core/time/time_linux.odin:
Tick against Time, both an i64 of nanoseconds, over MONOTONIC and REALTIME,
with the seconds-valued face derived rather than a second syscall. Three C
functions here and six Flan names over them, which is the rule flan_rt.c's own
header states -- a primitive is the only thing implemented twice.
The monotonic origin is the first read of the clock in the process, not boot,
and that is the one decision worth arguing. CLOCK_MONOTONIC counts from boot,
so on a machine up a hundred days the raw value is past 2^53 nanoseconds and
monotonic-seconds would lose sub-microsecond resolution depending on the
machine's uptime rather than on anything the program did. Latched to first
read it stays integer-exact for a hundred days of process life, and it also
matches what a game already has: raylib's GetTime is seconds since
InitWindow, so the two numbers now mix without a conversion at every site.
sleep-ns loops on EINTR, because otherwise a signal cuts the wait short and a
frame loop wobbles for reasons nothing in the program explains. It is
documented as at-least and not as a frame limiter; the shape that actually
paces a loop is a deadline recomputed from monotonic-ns each turn, and the
comment says so where somebody will read it.
getenv answers an (Option [u8]) viewing the process environment, which needs
no allocator and no free and is safe precisely because nothing in this
language can call setenv or spawn a process. The absent case rides in the
length rather than in the pointer: there is no null test to write, since a
(Ptr T) here always addresses something, so flan_getenv answers -1 and a
pointer at a valid empty string and the Flan side tests arithmetic.
The runtime additions are a single block at the end of flan_rt.c, with
<time.h> inside it for the reason <errno.h> sits beside the file section.
programs/time.flan asserts invariants and never a reading -- t2 >= t1, a sleep
that did not return early, a date after 2020 and before 2100 -- because the
same file is in the corpus @x86 builds twice and diffs, so a timestamp would
fail a correct compiler on its second run.
The prelude's declare surface was five f32 functions, and the five were there
because somebody needed each one. Everything else a caller wanted was written
as a declare at the top of their own file -- the identical libm call with none
of the caveats written down.
So the rest of libm is here: tan, the three inverses, the three logarithms,
exp, fmod, hypot, cbrt, fabs, and an f64 face for every one of them including
the five that already existed. A declare is a line, a symbol already on the
link, and nothing in either backend, which is why this was cheap enough to do
completely rather than one function at a time.
The f64 half is not decoration. f32 is what a position is; f64 is what a
measurement is -- the clock, parse-f64, format-f64, any sum over more than a
few thousand terms -- and having only the f32 face forced a cast down and back
at each of those boundaries, which is where the precision went.
The paragraph the sqrt note draws for itself is now drawn once for the family:
IEEE-754 specifies sqrt, fabs, floor, ceil, round and fmod as exact or
correctly rounded, so those agree bit for bit across glibc, musl and
wasi-libc; it requires nothing of the rest, so the sand-grid rule covers all
of them unchanged. floor, ceil and round are Flan at f32 and libm at f64, and
that is not an inconsistency: the f32 bodies work because every f32 with a
fraction fits in an i32, and at f64 that trick is gone.
abs-i32 and abs-i64 are Flan, one per width because min and max are builtins
and no generic covers the numeric types. pi and tau at both widths, written
out rather than derived so the compiler rounds each literal once.
programs/math3.flan covers it at values that are exact in binary, so nothing
pins one libm's last bit. The -O0 case is the one that matters: at -O2 LLVM
folds a call over two literals and leaves no symbol to resolve, which is how a
missing -lm hid the first time.
README documented four subcommands of eleven. The seven missing ones are
there now, with import-c and generate-c given a worked example each -- they
are the most valuable thing here that nothing documented at all.
An environment table, checked against the getenv sites rather than against a
list: thirteen variables, each with where it is read, plus the llc/clang
version coupling that breaks C-c C-c while flan build keeps working. The
FLAN_DEV_* set that flan dev hands itself across its own exec is named as
internal rather than left looking settable.
DISCUSS.md's survey of what the x86 backend had no plan for still listed the
whole condition family. x86.ml:1587-1615 lowers all of it and the survey is
104/104; the row is struck through and corrected in place, because other
files cite that table by position.
prelude.ml promised a core: package at milestone 3. Milestone 3 came and went
and the package did not, so the docstring states the limit instead of
promising a way out of it. The loader could carry one -- what is missing is
the decision about what core: means for a program that imports nothing.
Every size the containers compute is a product of a capacity the program chose
and an element size the checker did, and a product that wraps leaves a block
that fits beside a capacity that does not. The next write goes past the end of
an allocation a sanitizer was told to expect, which is the one corruption
nothing in the suite could have found.
The Vec's growth, the Pool's two blocks and their sum, the map's five runs and
the budget check now go through checked arithmetic. A size with no
representation reports along the path an out-of-memory already takes, with the
largest number the condition's field can hold, since the true one has none.
The test pins the case the guard exists for: an element of 2^33 + 1 bytes at a
capacity of 2^31 wraps to 2 GiB, which a heap allocator answers.
The 30s deadline in the reply reader was a literal and its message said only
that nothing had arrived. It is flan-dev-reply-timeout now, and the message
names the daemon buffer to look in -- a first compile on a cold cache is the
case that legitimately runs long, and the build log is what says so -- and the
setting to raise. Still never resent: a request the daemon took and died on
may already have run.
Package headers on all eight client files, so package-install-file on the
directory works and the client is not reachable only by load-path. The
daemon-buffer defcustom moves up beside the other buffer names, because the
reply reader now names it and the byte-compiler reads a file in order.
with_errors had no Sys_error arm, so flan check nosuch.flan ended in OCaml's
default handler; the daemon has had that arm since before the CLI did. A
Not_found backstop joins it — nothing reaches it today, and the day something
does the failure should name the file rather than say nothing at all.
flan run handed every flag it did not understand to the compiled program:
flan run game.flan --debug built at -O2 and gave the game a --debug. Build
flags are now the build's, -- ends them, and an unknown dash argument before
-- is refused by name with -- named as the way to mean it for the program.
-O0 through -O3 get a spelling on build and run, which they did not have at
all: Build.default pinned -O2 and --debug was the only route to anything
else. Four levels and not five, because -Os is clang's and llc rejects it,
and the same string reaches both. --debug with a higher level is refused
rather than quietly overruled by Build's own -O0.
Three suite runs left "Fatal error: exception Flan.Loc.Error(_)" on stderr:
OCaml's default handler knows nothing about the diag record, so a process
that does not catch prints a constructor name and none of the message. The
trigger was a corpus file the test binaries check directly and nothing there
wraps. Registering a Printexc printer changes no control flow and costs the
drivers that do catch nothing; it only makes the corpse legible.
check_main raised against Loc.unknown, so both of its refusals opened with
<unknown>:0:0. env.locs is the table of where each type was declared and a
function is not in it, so the location comes from the declaration list the
caller already holds. A main that arrived without a defn keeps the unknown
span rather than being given an invented one.
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.
The refusal was on the defvar path alone, so (defconst c U (U {.i 1}))
still came back from the emitter as "a global's value must be a
compile-time constant — this one is computed", which is true and says
nothing about unions. Both kinds of global reach the same encoder, so
both get the same message.
It is decided on the checked value rather than on the declared type now,
which is what lets the one initialiser that *is* a constant through: (U
{}) is all-bytes-zero, the same value a declaration with no value gets,
and refusing it would have been telling someone to write the thing they
had written.
The name freed up by the rename now means what C means by it: the members
overlay one storage, the size is the largest of them, the alignment the
strictest, and nothing anywhere records which one was written. It serves
two things that wanted it. Binding a C header means holding the union the
library holds and reading whichever member the library's own tag says is
live -- a tag Flan cannot see, because the rule relating them is prose in
a manual. Overlaying an f32 on a u32 to look at its bits is the other,
and it is the same read.
So that read is defined rather than refused. This is the one place in the
checker where bytes win over safety on purpose, and the alternative was
not a safer language, it was no feature: type punning *is* reading the
member that was not written. The promise is the one C's implementations
make and C's standard does not -- the layout is the target's, the bytes
are the bytes, a read is a reinterpretation of them -- and what is not
promised is anything about bytes nobody wrote, where a member wider than
the one last stored reads a tail that is indeterminate exactly as a
struct's padding is. ZII narrows that to almost nothing: a union starts
all-bytes-zero unless uninit says otherwise.
uninit on one is allowed, unlike on a defdata. The refusal there was
never about garbage; it is that a tag steers, and a tag no case names
falls past every comparison in a match into a block LLVM may treat as
unreachable. An untagged union steers nothing.
Which is also why three things are refused, each for a reason that does
not expire with a milestone. No move-only member: nothing knows which
member is live, so nothing can tear one down, and unlike the struct and
defdata refusals this is not waiting on recursive teardown -- there is no
fact for teardown to read. No bool at any depth: an i1 loaded from a byte
that is neither 0 nor 1 is a value the optimiser may assume cannot exist,
and a union is the only type that can produce one. No defdata at any
depth, for the reason uninit gives, arriving the other way round. An
Option member is fine and the walk says why: its match is a tag test and
a branch, not a chain with an unreachable tail.
Two members in one literal, a match on a union, a union map key and a
member written into a global initialiser are each refused by name.
A union is a field list whose every offset is zero, so it travels as a
Tast.structure and the checker, the emitter and the x86 backend each grow
one table rather than one shape. A value is a zeroed temporary and a
store -- Set over Pfield, which every backend already has -- so there is
no new IR node and no layout rule spelled out a second time per backend.
The LLVM type is the blob clang gives a union, the DWARF is
DW_TAG_union_type with every member at zero, and the printer names the
type and does not walk it: it cannot know which member is live, and one
of them may be a pointer.
cimport can now check what it could not. A C record holding a union
member was not recorded at all, so the defstruct beside it went unchecked
rather than checked wrongly; a named union member resolves to a defunion
now and the whole record is compared field by field. The defunion itself
is compared against the header's union as a set and not in order --
every member is at offset zero, so a permuted one is the same type and
reporting it would be a finding that is not one -- while a member the
header has and Flan lacks is reported, because that is what changes the
size. A defunion against a C struct, or a defstruct against a C union,
is reported in both directions. An anonymous union member is still
skipped, and the comment now says that the gap is on the Flan side:
there is nothing to declare.
Emit.program ~hidden and ~dev are opposites: a dev build exports its cells,
globals and flan.abi.* so that a redefinition module can bind against them, and
hiding those would give a host that links, runs and silently installs nothing.
Nothing in the types stopped the combination being written, so it fails with a
sentence instead. Build.macro_module is the only caller that asks for hidden and
it never asks for dev.
The handoff's verification is narrowed to what it actually covers: the 540-file
IR diff is about Emit.program's default, and the new path is read off nm -D on
the linked module. It also now says why sand-headless.flan is the fixture that
checks 65d14f4 -- it reaches rl/with-drawing through an import, which is the
package-macro shape the reproduced bug had.
flan dev's merged build is the program and the compiler in one -rdynamic
executable, so it exports every flan.* body it has, and ELF gives it precedence
over anything dlopened afterwards. The compiler expands a macro by dlopening a
module into that same process, and the module is built by Emit.program whatever
backend the session uses -- so under --x86 the caller was LLVM's and the body it
landed in was the dev backend's, which is a crossed pair. It died with SIGSEGV
inside flan.[clamp] during the first expansion, before the program had run a
line, and Dev.start refused the combination rather than do that.
Build.macro_module now asks Emit.program for hidden visibility on the module's
own Flan definitions. There is nothing left for the host to interpose, and the
flan.macro.* thunks stay exported because dlsym is how the compiler reaches
them -- nm -D on the built module lists those three and nothing else of Flan's.
The -Wl,-Bsymbolic that had been binding everything locally since 65d14f4 goes
with it: the module links its own flan_rt.c, and binding that locally aimed its
calls at a runtime flan_rt_init never ran on, with a null flan_exit_hook, so a
trap raised inside an expansion would have exited the process instead of parking
it.
Nothing about the host moved, which is what keeps redefinition modules reaching
its cells, its globals and flan_dev_cell. hidden defaults to false, and the 540
IR files this compiler emits for the test corpus are byte-identical to the ones
before it.
test_dev.ml's assertion that the merged daemon refuses --x86 becomes the session
it was standing in for: dev-macro.flan calls a prelude macro at the top level,
so the daemon coming up at all is the old crash not happening, and one build
then carries C-x C-e, a C-c C-c whose body calls a macro again, the park and the
rerun.
--two-process has no parked thread to wake. Its program is a child, and a
child that finishes is gone, so running main again is not something that shape
can do — and saying "the program is already running" would send somebody back
to try again after it had exited. It names itself instead.
--x86 arrives here too and is the reason this is worth a round trip rather
than none: --x86 refuses the merged daemon, for the -rdynamic reason the case
below already records, so every x86 dev loop is a two-process one and this is
the answer it gets.
Flan's tagged sum has been spelled defunion since it landed, which was
accurate right up until the language wanted C's untagged union as well.
Both cannot be called the same thing, and the tagged one is the one with
an alternative name that says what it is: a case, its fields, and a tag
that steers which case is live is a data type, not a union.
So the form is defdata everywhere -- the parser, the AST, the checker,
both backends, the prelude's Form, the editor's font-locking and imenu,
the docs and every .flan file in the tree. The internal vocabulary moves
with it: Tast.union is Tast.data, uname is dname, the tables the checker
and the emitter keep are datas. Leaving them would have inverted the
words permanently, with surface defunion meaning one thing and
env.unions meaning the other, which is exactly the kind of drift the
comments in those files exist to prevent. What did not move is case,
variant and vfields: a tagged sum still has cases, and it still has one
live at a time.
defunion is not kept as an alias. An alias would compile the day the
untagged form lands and mean the opposite of what it used to -- the same
silent misparse that made defn's return type mandatory, and worse,
because the reader would have no reason to look. The old spelling is a
named refusal instead, parse/defunion-renamed, which says what it is now
called and that the name is reserved for something else. It fires on the
head alone, so (defunion U [A B]) -- which would otherwise have parsed
cleanly as one field A of type B -- is refused with the rest.
basis had the same false promise the eval note did. It branches on the break
state, which answers "running" while the program is parked — the agent's
listener is alive and nothing has stopped — so disassemble reported that a body
delivered while parked installs at the next frame boundary, which is not a
boundary the program will reach until somebody runs it again.
And flan-rerun had no autoload. The keymap binds it, and flan-mode.el says in
as many words why every command there needs a real autoload rather than a
declare-function: a user who loaded only flan-mode would otherwise find the key
bound to nothing at the exact moment they most want it.
You run a program under flan dev, it opens a raylib window, you close the
window, main returns — and there is no way to get another window short of
flan-dev-restart-program, which throws away the build, the session and every
global with it. In Common Lisp or Clojure the image outlives main, so you call
it again. The process here already outlived main: the exit hook flushed, closed
stdout and sat in for (;;) pause(). Nothing could wake it.
So main() is a loop. The hook records the status and longjmps back into a
setjmp in main() — there is no return available, since flan_exit is reached
from wherever the program happened to be — and the thread waits on a condition
variable until the new rerun op signals it. The main thread is the one that
runs main again: a window belongs to the thread that opened it, and on macOS to
the first thread of the process. A longjmp pops no frame, so the park first
empties the handler stack, the restart stack and the shadow frame chain, each
of which was a chain of allocas in stack the next run is about to write over.
Nothing else is reset; the second run reads whatever the first left in the
globals, which is the semantics that was asked for.
Closing stdout had to go with it. That was how the compiler learned the program
was done, but a pipe delivers EOF once, so the signal and the program's output
were the same resource and spending it left the second run with nowhere to
print. The descriptor hazard the old code reopened /dev/null for goes away with
the close that caused it. Liveness is asked for instead, through a weak symbol
in the same style as the agent's, and is now three states rather than two: Live,
Parked and Gone. Every guard branches on that before consulting the break
state, because the agent's listener answers "running" while the program is
parked and telling somebody whose program has finished that it is running is
worse than saying nothing. Only eval accepts a parked program — it queues and
waits for nothing, and the queued module installs at the first frame boundary
of the next run, so a body can be fixed while parked and the re-run executes
it. Everything else needs a frame boundary or a stopped stack, has neither, and
says which, naming the command that gets the program back.
A re-run while the program is running is refused rather than queued: the test
and the signal happen under one mutex, so two mains writing the same globals at
once never starts.
:parked rides on every reply beside :stopped, for the reason :stopped does —
finishing is as unannounced as stopping, more so when the way it happens is a
mouse click on a title bar. Emacs shows flan:parked in the modeline and binds
flan-rerun to C-c C-M-x.
