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AILang/examples/std_either_list.ail
Brummel 76b21c00eb feat(lang): eliminate the Implicit ownership default — totality + the drop-soundness it demasks (#55)
Deletes `ParamMode::Implicit`. `ParamMode` is now `{Own, Borrow}`:
every fn-type slot on every signature carries an explicit `own` or
`borrow`, no defaulted position survives anywhere (model 0008 §2,
spec 0062). The parser rejects a bare fn-type slot; `borrow-return`
and `borrow-over-value` reject at the signature; the corpus is
migrated to minimal-ownership modes (consumed ⇒ own, read-only-heap
⇒ borrow, value ⇒ trivial-own). The documented `Implicit`-ret-mode
leak is fixed: an owned heap return now drops exactly once (live=0,
acceptance criterion 5).

This was the easy half. Removing the default ACTIVATED a family of
drop paths that `Implicit` had silently skipped — the pre-cutover
language was leaking (and in places mis-dropping) here rather than
crashing, because an Implicit scrutinee turned the drop off. Making
the modes explicit (Own) turned those paths on and exposed two
latent-bug clusters, all fixed RED-first as part of this cutover:

Drop-soundness family (four legs):
  A. lit-sub-pattern double-free — the desugar re-matched the same
     owned scrutinee in the lit fall-through; fixed by grouping
     consecutive same-ctor arms into one match (bind fields once),
     in ailang-core desugar.
  B. Cons-husk leak on non-tail arm bodies — the lit-sub-pattern
     desugar rebound the owned scrutinee via `Let $mp = xs`, which
     bumped consume_count and suppressed the existing fn-return
     partial_drop. Fixed by not rebinding a bare-Var scrutinee
     (one husk-freeing mechanism, not two).
  C. polymorphic `drop_<T>` rc_dec'd monomorphised value fields —
     the per-ADT drop fn was emitted once from the polymorphic
     TypeDef, defaulting type-var fields to ptr and rc_dec'ing
     inline Ints (segfault). Fixed with per-monomorph drop
     functions (new ailang-codegen::dropmono): the drop set is
     collected from the lowered MIR, value-type fields are skipped,
     heap fields still freed once; monomorphic-concrete ADTs keep
     their byte-identical un-suffixed drop symbol.
  D. static Str literal passed to an `(own Str)` param — the
     literal lowers to a header-less rodata constant; the callee's
     now-active rc_dec read its length field as a refcount and
     freed a static address (segfault). Fixed with the missing
     fourth StrRep::Static→Heap promotion in lower_to_mir's App arm,
     gated on Own mode (borrow args stay static, no regression).

over-strict-mode lint over-fired: it suggested `(borrow V)` for
value-typed params (which `borrow-over-value` rejects — own is the
only legal mode there) and fired on `(intrinsic)` bodies (whose
consumption the linearity walk cannot observe). Tightened to skip
both; contract 0008 updated to the narrowed firing scope.

Irreversible step — canonical-form hash reset (model 0008 §6,
acceptance criterion 6). Every signature now carries explicit modes,
so the hashable canonical JSON changed for every module. RATIFY:
the corpus-wide hash-pin reset (hash_pin, prelude_module_hash_pin,
mono_hash_stability, eq_ord_e2e, embed_export_hash_stable, the
ct4/iter*/loop_recur schema-extension pins) and the list ir_snapshot
golden were regenerated once, deliberately, as the intended one-time
consequence of removing the mode elision from the canonical form —
not a regression. Each regenerated hash verified deterministic across
two runs.

Also fixes a pre-existing latent failure surfaced by the verification
gate, unrelated to this cutover: the `every_contract_names_a_resolvable_
ratifying_test` resolver (design_index_pin) could not resolve the
" + " dual-link ratifying-test form (`uniqueness.rs + linearity.rs`)
that the #57 audit-close (dfdc65f) introduced — it shipped red on that
commit. Resolver taught the dual-link form, mirroring its sibling.

Verification: cargo test --workspace = 731 passed, 0 failed (twice,
stable); e2e 102 passed, no binary exits non-zero (corpus crash-free);
grep-clean for Implicit/fn_implicit/mode_eq across crates; every drop
fix confirmed via emitted IR + AILANG_RC_STATS balance on the head==K,
head!=K, and Nil paths. Three BLOCKEDs en route (the unsound first
husk-dec attempt, the over-strict derivation premise, the leg-B fix
direction) were each treated as a real design/spec gap and rediagnosed,
not patched over.

Supersedes #54 (return-position-only leak patch). Precondition #57
(linearity hardening) was already met. Spec docs/specs/0062, plan
docs/plans/0121.

closes #55
2026-06-02 00:03:46 +02:00

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; Iter 15g — fifth stdlib module: first 3-way cross-module fn set.
; Imports std_list, std_either, std_pair simultaneously. All three
; combinators dispatch over List<Either<e, a>>; partition_eithers
; additionally returns Pair<List<e>, List<a>>. Stresses
; monomorphisation across List × Either × Pair, cross-module ctor
; resolution at qualified term-ctor sites, and the 16a desugar
; layer at depth-2 nested Ctor patterns (in `lefts` / `rights`).
(module std_either_list
(import std_list)
(import std_either)
(import std_pair)
(fn lefts
(doc "Project the Left payloads of a list of Eithers into a List<e>. Order-preserving. Uses the 16a nested-Ctor pattern to inline the inner Either dispatch within each Cons arm; the trailing wildcard arm seals the desugar's fall-through chain into a List<e> rather than the synthetic Unit fallback.")
(type
(forall (vars e a)
(fn-type
(params (own (con List (con Either e a))))
(ret (own (con List e))))))
(params xs)
(body
(match xs
(case (pat-ctor Cons (pat-ctor Left l) t)
(term-ctor List Cons l (app lefts t)))
(case (pat-ctor Cons (pat-ctor Right _) t)
(app lefts t))
(case _ (term-ctor List Nil)))))
(fn rights
(doc "Project the Right payloads of a list of Eithers into a List<a>. Symmetric to lefts; same nested-Ctor + wildcard-tail pattern shape.")
(type
(forall (vars e a)
(fn-type
(params (own (con List (con Either e a))))
(ret (own (con List a))))))
(params xs)
(body
(match xs
(case (pat-ctor Cons (pat-ctor Left _) t)
(app rights t))
(case (pat-ctor Cons (pat-ctor Right r) t)
(term-ctor List Cons r (app rights t)))
(case _ (term-ctor List Nil)))))
(fn partition_eithers
(doc "Partition a list of Eithers into a Pair<List<e>, List<a>>: lefts on the left, rights on the right. Single pass via direct recursion; the recursive result is destructured once and the head dispatches into the matching side.")
(type
(forall (vars e a)
(fn-type
(params (own (con List (con Either e a))))
(ret (own (con Pair (con List e) (con List a)))))))
(params xs)
(body
(match xs
(case (pat-ctor Nil)
(term-ctor Pair MkPair
(term-ctor List Nil)
(term-ctor List Nil)))
(case (pat-ctor Cons h t)
(let rest (app partition_eithers t)
(match rest
(case (pat-ctor MkPair ls rs)
(match h
(case (pat-ctor Left l)
(term-ctor Pair MkPair
(term-ctor List Cons l ls)
rs))
(case (pat-ctor Right r)
(term-ctor Pair MkPair
ls
(term-ctor List Cons r rs))))))))))))