A dev cell carries its body's signature word beside the body, every call through a cell (and every function value taken from one) compares it with the word the site was compiled for, and the session lists the stale callers by file and line on the reply. Both backends, both installers; release builds have neither the word nor the compare.
FIX.org, NEXT.md, DISCUSS.org, docs/DISCUSS.md and the session handoff at the
root are one TODO.org now: 293 entries under seven subsystem headings, each
carrying an org keyword that says where it stands. A DONE entry is a few lines
saying what was decided and what that rules out; the reasoning that would not
compress — the embedding spike and the four reports the hand-written x86
backend was built from — moved into docs/BUILT.md instead, and its entries
point there in one line.
Every entry was checked against the tree before it got a keyword, and the
prose was wrong in both directions. Things the deleted files called open were
built: the first-evaluation stall, main being redefinable, macro parameter
lists, the type-limit constants, the array constructors, the byte fills,
inc/dec, the discard's fontification, the Emacs buffers, rt_die's _exit, the
backtrace surface, and the acceptance failure that could print and still exit
zero. Things they called done were not: the backend reports' no-plan buckets
had gone stale in the other direction, the value-dependent defvar was
superseded rather than built, and macro-expansion source locations are on an
unmerged lane, so that entry is NEXT and names the branch.
Every comment that cited one of the five by name now cites a heading that
exists, in TODO.org or in docs/BUILT.md. The session reports under
docs/handoffs/ keep naming the files they worked on, because rewriting them
would falsify what those sessions did; each carries a note saying where the
content went.
The four refusals the function-value lane wrote down are now three and a
half: capture is a feature, the escape is the refusal in its place, and a
struct field or a global of function type is refused for the same zero as
before with a sharper reason behind it. The handler note is amended
rather than deleted -- its reading was right, and saying so is worth more
than a clean paragraph.
The convention section carries both rulings, the name and every name it
beat, the warning that CFn is not C interop today, the four reasons to
reach for it, what was measured rather than asserted about an ordinary
defn, and the wasm32 finding that killed the first design -- being
exactly typed is checkable by a verifier and the alternative was an
argument from a calling convention.
FIX.org carries the rulings verbatim, what the escaping lane inherits and
changes, the thunk's environment holding a code pointer rather than a GC
object, and two things recorded and not built: a CFn under a future
--no-conditions reaching C's exact convention, and CFn in a struct or a
fixed array, which ZII refuses and capture has nothing to do with.
The author: "I think I prefer length over len, because then I'll use len as
the variable name". One arm in check.ml, one row in the table beside it, and
every (len x) in lib, test, examples, vendor, spike, docs, web, emacs,
plan.org and NEXT.md rewritten.
Shadowing and builtin/ had already taken most of the sting out: a (defn len
...) was legal and won in its own file, and builtin/len reached past it. What
was left is that len was still a builtin — the defn earned a warning, and a
wrapper had to say builtin/ at every inner call. Now there is nothing under
the short name: len is an ordinary identifier in every position, which is
what (let [len (length xs)] ...) wants.
length takes over as shadowing's worked example rather than the feature
losing one. shadow-builtin.flan, builtin-qualified.flan, pkgs/shadowed and the
builtin/ rows in test_flan move to it and go on testing shadowing.
A call to a len nothing defines is answered where an unknown function is,
after every table and after the shadowing guard, so a program with its own len
never reaches it. The sentence is said rather than guessed at — len and length
are three edits apart and the did-you-mean's net is one — and the call is
written back out through spell_arg, as-slice's spelling lifted out of it and
now shared, so what is printed compiles.
sand.flan:33 still calls the old name and is the author's to change; until it
does, test_acceptance and test_session abort there. Both were run green
against a copy with that one line changed. FIX.org says so.
rand-int, rand, rand-bool, rand-int-range and rand-float-range, at the widths
the author ruled: a u64 draw and an f64 in [0, 1). rand-seed and rand-state
keep their names. The four old names are not names, and each is refused by the
one that is, with a call that compiles — in both the call and the bare-name
position, because a Lisp-1 makes the second a real thing to write.
The generator's step is untouched, so a seed means what it meant. Its output
function is not: PCG-XSH-RR folded the state to 32 bits, and no honest u64 or
53-bit f64 comes out of 32 bits without a second step. PCG-RXS-M-XS 64 answers
64 from the same one, so all five still cost exactly one draw and a seeded run
is reproducible. The price, written where it lives: the permutation is a
bijection of the state, which is what 64 output bits from 64 state bits costs.
The sequence is therefore a different one, and programs/rand.flan pins it —
reproducibility across the five, the single-draw cost of each, the half-open
boundaries, and rand-bool's count over a thousand flips.
sand.flan is not touched. It calls rand-f32, so the cases that compile or
re-evaluate it skip themselves on the fixture rather than on a comment: fix
its two calls and every one of them runs again. Its hash is the old
generator's grid and gets re-taken then.
as-slice was a warning, not an operation. The input type already decides
which of the two things happens — a Vec can only be borrowed, an array or a
string can only be viewed, and no call site picks between them — so the second
name expressed no choice a reader could make. And it warned at the moment the
view is taken, which is the one moment nothing is wrong; the danger arrives
later, at the push. slice now takes a Vec at all three arities and as-slice
is gone.
(slice v lo) was free, and is the arity the Vec never had: the runtime already
reads a hi of -1 as "to the end", so the tail form passes the caller's lo and
the same -1 — no slot, no length read, no second evaluation. The merge is
entirely in the checker; the Vec path builds the flan_vec_as_slice call it
always built and neither backend has a line about any of it.
A Vec a call returned is refused at every arity, and not for the array's
reason. (slice (mk)) over an array dangles. (slice (make-vec)) does not — the
storage outlives the expression — but the header is a temporary, so nothing
can ever free the block. The refusal says that and names the let.
The name's own refusal sits in ordinary_call after every table, so a program
that defines an as-slice still reaches its own. It reads for somebody who has
never heard of the old name and writes the call back out, spelling each
argument that is a name or a number.
The warning moved to where it bites: BUILT.md gains a section beside the Vec
table and the push row points at it, spec-memory.md's Borrowing says the same.
Investigated and deliberately not built — a diagnostic for a live view at the
push. (reserve v 100) then a slice, a push and a read is correct code under
the contract the spec chose, so any flag on it is a false positive by the
language's own semantics rather than by an approximation. FIX.org has the
finding and the syntactic sketch that does not work.
"Is there a way to do dotimes or a loop in reverse?" — the answer was a
hand-written let plus set. Now it is (dotimes [i 9 -1 -1]).
Three arities: [i n], [i start stop], [i start stop step]. The stop is
exclusive in all of them, so [i 0 n] is [i n] — one rule, not two — and a
negative step counts down, testing with > instead of <.
A literal step of 0 is refused where it is written. One that is only a value
cannot be, so the condition asks the sign first and 0 falls out of it as a
loop that runs no times: terminating and deterministic, and free, because a
literal step still emits the single comparison it always did.
Each bound is evaluated once, left to right, before the counter exists: the
start into the counter, the stop into the hidden slot it always had, the
step into one of its own unless it is a literal.
Still a special form, still a Let and a While with the step in the latch, so
neither backend learned anything — the new program prints the same thing
under --x86 and at -O0. load.ml's Form-level walk had to learn more than one
bound for the same reason parse.ml did; it is part of this feature and not a
bug that was sitting there, because before this a three-bound dotimes was a
parse error long before that walk could reach it.
The trio the author decided on 2026-09-20 is now all built: def is CL's
defparameter — its initialiser runs on every daemon re-run, unguarded, so
an edited initialiser repaints the same storage on C-c C-c plus re-run —
defonce (Clojure's name for CL's defvar, per the author) initialises once
behind the .init~once. flag, and defconst stays the image.
One parse arm reads both forms; the difference is Ast.reinit, carried to
Tast.global's grerun. Emit.startup_plan gives a def no guard flag, and
Check.check_global lifts every def initialiser — zero and literal
included — into global/<n>, so the host's startup reaches it through the
function cell and a re-evaluated def swaps it (Session's def_inits;
Emit.redefinition declares the cell for a non-sibling target). The old
defvar spelling is refused with the rename and both compiling spellings,
and every program, test, doc and editor list is swept — except sand.flan,
the author's live WIP, whose seven defvar lines are flagged in FIX.org
and keep its three dependent tests red on this branch.
The INSERTIONSORT crash, all three rulings (FIX.org 2026-09-20):
- (bytes s) allocates a writable copy through the allocator surface —
context or (bytes s a), StorageExhausted with retry, a registry note in
dev builds (flan_bytes_dup, lowered like vec-new). (bytes-view s) is the
old zero-cost reinterpret, renamed, read-only by convention; every
in-repo reader swept over to it. (string b) unchanged.
- String constants were already read-only on both backends at -O0; now
pinned — bytes-copy.flan rows on LLVM/-O0/--x86, and dies_segv rows
asserting the write-through-view trap on both backends.
- A dev build installs a SIGSEGV/SIGBUS handler by the same dev-only
constructor slot that arms the registry: one line naming the address and
the innermost frame, then the trap-hook park — stopped, not dead, the
daemon serving. No agent: message and re-raise. Release builds untouched.
Pinned by trap_park over dev-segv.flan.
A narrower scalar at a $t a slice already fixed widens into the fixed
type — the same cast a monomorphic parameter applies — where the old
rule refused both directions. One accepts pin, one runtime line in
int-generic.flan, and the web page's predicate table catches up: five
predicates, integer? at the head, and the entailment chain grown one
link.
The fifth predicate: integer? admits every integer kind and no float,
entails numeric? (and through it ordered? and equal?), and gates what
only integers support — the bitwise fold asks for it, the shifts admit
a bounded variable under it, and the float literal in an integer? body
is refused in the bound's own words. The literal arm needed nothing:
the entailment admits an integer constant under either bound.
abs-i32 and abs-i64 collapse into one integer?-bounded generic whose
i32/i64 copies even keep the old symbols; abs-f32/abs-f64 stay as the
float spellings because the right float abs is a sign-bit clear no
integer body spells, and (abs 1.5) now refuses naming the bound — the
where clause is checked before the name-collision check, which used to
answer that call with 'abs-f64 is already defined'.
Mixed widths at one $t join at the wider type now, in either argument
order — the author reversed the refuse-both rule on 2026-09-20. A
joinless pair is deferred and re-asked against the final binding, so a
later wider argument settles u32-vs-i32; u64-vs-i64 still refuses, and
a container-bound variable still binds exactly. The out-widened
arguments catch up through the ordinary Cast.
Two review follow-ups folded in: a struct field's unknown-lowercase
message stops suggesting a parameter vector it does not have, and the
tyvar-at-dyn message says defgeneric/defmethod in words instead of a
schematic that does not compile.
The unwinding handler, which spec-conditions.md named and left unwritten while
it asked whether the thing should be a macro over the two operators that were
already here. It should. (handler-case B [(T [c] A)]) is checked as
(restart-case (handler-bind [(T [c] (invoke-restart 'R c))] B) (R [c T] A))
with R a name the form makes up for itself, which is Common Lisp's own
definition of the operator and means neither backend needed a line.
What that buys is not economy, it is the correctness of the parts nobody can
see. The defers between the signal and the form run, and the allocator a
with-allocator rebound is put back, because a transfer already does both for
every frame it leaves. The body and every clause agree on one type, because a
restart-case's body and clauses already do, and a clause that disagrees is
refused with the same message an if with disagreeing arms gets. A condition no
clause lists installs no frame that matches it and goes on outward untouched.
A clause sees the establishing function's locals, which a handler-bind clause
cannot, because a restart clause runs where it was written.
The body comes first and the clauses after it, the opposite of handler-bind's
order: one reads as something put around a body and the other as a body with
answers hung off the end of it. The restart the two halves meet over is named
after the function and numbered within it, and it has to be unique per form,
because two nested handler-cases sharing a name would have the inner frame
shadow the outer one and land a condition at the wrong place.
The refusals name handler-case rather than the machinery underneath it, which
is why check_handler_bind and the restart clauses now take the word the reader
wrote. A break loop entered under a handler-case still lists the made-up
restart, and taking it there is refused loudly rather than answered wrongly;
hiding it would mean a field in a frame layout spelled out in three files.
The survey program runs the same under LLVM, at -O0 and under --x86: normal
completion, a caught condition, one nobody listed passing through with the body
carrying on, both defers on the way out, the two nestings against handler-bind,
a clause that signals and is caught outside the form it belongs to, and a
with-allocator whose restore is on the transfer path.
The !-means-mutates convention distinguished nothing — there is no
immutable counterpart to contrast with — so every mutating name drops
the mark: sort, sort-by, sort-bytes, swap, reverse, append, append-i64,
append-f64, encode-rune, split-next, map-remove, map-next, and the test
helpers beside them. Two could not simply shed it: map! is map-in-place,
because map is the into transform's word and means the non-mutating
thing; put! is put-at, because put is the Map builtin. The ?-means-asks
convention stays. Dated records keep the old spellings; watch.clj's
reset-spies! and the other Clojure names are not ours to rename.
`-dev-` was in every Emacs symbol this client owns and meant nothing to anyone
typing one: the daemon is `flan dev` at a shell, but from inside Emacs there is
no other kind of connection to distinguish it from. `M-x flan-dev` is now
`M-x flan`, `flan-dev-quit` is `flan-quit`, the private prefix `flan-dev--` is
`flan--`, and every defcustom follows — ninety-odd symbols, with the two files
renamed to emacs/flan.el and emacs/test-flan.el so the file names say the same
thing as the symbols in them.
No aliases. Renaming a defcustom breaks a config that names it and there is no
way around that; the repo has no precedent for softening one, and an alias left
behind is what keeps a rename from finishing. MANUAL.md says the old names are
gone and how to fix a config, which is the whole of the migration path.
Three strings are not symbols and keep their spelling: `.flan-dev.sock`, which
bin/main.ml writes and which a renamed variable searching for a renamed file
would simply never find; and the two buffer names `*flan-dev*` and ` *flan-dev*`,
which name the `flan dev` subcommand's own output rather than anything in elisp.
`flan dev` with a space is the CLI and is untouched everywhere.
The entry point also stops asking a question it already has the answer to. From
a buffer visiting a .flan file it starts that file; from anywhere else it reads
one from the minibuffer as before; `C-u` reads one either way, which is how you
start a second program without leaving the first. The current buffer is still
the only source of the default — the bug where a previous project won over the
buffer you were in was fixed by removing `flan--file` from that position, and
nothing here puts it back.
Four checks on the `interactive' form, evaluated on its own rather than by
calling the command, because calling it would build and launch a program and
the question is only which file the form arrives at and whether it had to ask.
A fifth asserts that nothing answers to the old names. test/test_emacs.ml loads
the test file by path and test/test_session.ml names the client file in a
comment, so the rename reaches those two lines; nothing else outside emacs/ and
the docs moved. Verified by byte-compiling every file
clean and by `dune test` and `@page`.
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.
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.
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.
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.
