Decision 8 ships. Term::App and Term::Do gain tail: bool with
serde-default false and skip-when-false serialisation. New
typecheck pass verify_tail_positions enforces tail-position rules
(Scheme-style propagation through match arms, seq.rhs, let body,
lam body). Codegen emits musttail call for marked App calls.
Hash invariance verified: only the two migrated print_list defs
(list_map_poly.print_list, sort.print_list) changed hashes; all
other defs across all 18 fixtures kept bit-identical hashes —
confirms the skip-when-false serialisation rule works.
Tests 76 -> 79: tail_call_in_non_tail_position_is_rejected,
tail_call_in_tail_position_is_accepted, plus an IR-grep e2e test
asserting that print_list's recursive call site emits musttail
in the lowered IR. Existing 25 e2e tests unchanged in behaviour
(map -> [2,3,4], sort -> sorted list).
IR evidence at the recursive site:
%v7 = musttail call i8 @ail_list_map_poly_print_list(ptr %v6)
ret i8 %v7
Two deviations called out in the implementer report and JOURNAL:
1. tail-do uses tail call, not musttail. Cross-type return
(runtime helpers return i32, AILang Unit is i8) would have
LLVM reject musttail. Path is implemented but not exercised
by any current fixture; proper fix is runtime-helper signature
change, punted.
2. block_terminated flag in codegen so tail-call emit
(musttail call + ret) doesn't get a duplicate trailing ret
from surrounding code (match-arm phi, fn-body, lambda thunk).
Internal plumbing; required for IR well-formedness.
Form (A) productions now at ~30, exactly the constraint-1
budget. Future surface additions need to retire something or
explicit-budget-rebalance in DESIGN.md.
GC notes from implementer survey land in JOURNAL:
- Allocations cluster in lower_ctor; every term-ctor does
malloc(8+8n).
- Tail recursion does not reduce alloc pressure, only stack.
For map-style ctor-blocked recursions, allocation IS the
bottleneck.
- Per-fn arena is sound only when fn return type contains no
boxed ADT. Most current fixtures violate this.
Plan 14f: Boehm conservative GC (GC_malloc, -lgc) as a first
cut. Single-iter integration, no AST/schema change. Stress
test: build a 100k Cons list, observe RSS doesn't blow up.
After 14f the language is feature-complete enough for stdlib
work (15a).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Dogfood payoff for parameterised ADTs (13a/b/c). Adds the first
program to nest a nullary ctor of a parameterised ADT inside a
parent ctor (Cons(Int, Nil)) and to call a polymorphic recursive
higher-order fn over a recursive parameterised ADT.
Fixture (examples/list_map_poly.ail.json):
- data List a = Nil | Cons a (List a)
- inc : (Int) -> Int = \x. x + 1
- map : forall a b. ((a) -> b, List<a>) -> List<b>
recursive, instantiated at (Int, Int)
- print_list : (List<Int>) -> Unit !{IO}, recursive
- main builds [1,2,3], maps inc, prints each: "2", "3", "4"
E2E test list_map_poly_inc_then_prints in crates/ail/tests/e2e.rs.
Bug fixed (crates/ailang-codegen/src/lib.rs, +30/-9):
synth_arg_type used Type::unit() as placeholder for ADT type
vars that the ctor's args couldn't pin (Nil for List<a>).
Inside Cons(Int, Nil), unify_for_subst then bound a=Int from
the head and collided with a=Unit from the tail. Replaced the
placeholder with a synth-only wildcard Type::Var{name:"$u"}
mirroring the checker's $m metavar convention; unify_for_subst
short-circuits on $u-prefixed arg-side vars (accept without
binding, let a sibling pin the var).
No schema or API change. No new variant. Tester's recursion
hypothesis was refuted by debugger via a non-recursive
Cons(7, Nil) repro before the fix landed.
Tests: 25/25 e2e (was 24). All Iter 12/13 regressions green.
cargo doc --no-deps zero warnings (workspace invariant from
13d/e/f preserved).
Three-agent flow (tester -> debugger, no implementer needed
since the fix was inside debugger's <50 LOC scope). Process
note in JOURNAL.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Brummel