AILang/docs/journals/2026-05-13-iter-24.3.md

iter 24.3 — fn print polymorphic free fn + E2E + DESIGN.md sync; milestone 24 close

Date: 2026-05-13 Started from: c04c07f Status: DONE Tasks completed: 8 of 8

Summary

Ships fn print : forall a. Show a => (a borrow) -> () !IO in examples/prelude.ail.json with explicit-let body \x -> let s = show x in do io/print_str s. The let-binder is structurally pinned by crates/ail/tests/print_mono_body_shape.rs (post-mono print__Int.body is Term::Let → Term::App(show__Int) → Term::Do(io/print_str)). Three new E2E fixtures + tests verify the full path: show_print_smoke (4 primitives) and show_user_adt (data IntBox + instance prelude.Show IntBox + print (MkIntBox 7)) both compile, run, and produce expected stdout; show_no_instance fires a Show-aware NoInstance diagnostic with the canonical DESIGN.md cross-reference. DESIGN.md §"Prelude (built-in) classes" flips print from "ships in 24.3" to "shipped in iter 24.3" with the explicit-let body + pin reference. DESIGN.md §"Float semantics" gains a Show-Float NaN-spelling cross-reference paragraph. Roadmap P1 "Post-22 Prelude — Show + print rewire" entry checked off; new P2 entry "Retire io/print_int|bool|float effect-ops + migrate example corpus to print" inserted at top of P2. Three plan-defects-fixed- inline surfaced when running the user-ADT E2E: (a) MonoTarget:: FreeFn::type_args were carrying bare type-cons references that broke the post-mono walk's registry lookup when the synthesised body lived in a different module from the type — fixed by normalising via workspace_registry.normalize_type_for_lookup at two mono.rs collection sites; (b) codegen's cross-module fn resolution went through import_map, but post-mono synthesised bodies may reference modules their source template didn't import — fixed by falling back to direct module_user_fns lookup at three codegen sites (resolve_top_level_fn, lower_app cross-module arm, synth_with_extras Var arm); (c) the synth FreeFnCall arm didn't push residuals for declared constraints, so Show (Int -> Int) never reached the typecheck-time discharge logic — fixed by walking Type::Forall.constraints at the FreeFnCall site and pushing one residual per constraint with the fresh-metavar substitution. Full cargo test --workspace 556 passed / 0 failed (was 552 post-24.2, +4 new = 1 print_mono_body_shape + 2 show_print_e2e + 1 show_no_instance_e2e). bench/cross_lang.py clean; bench/compile_check.py

• bench/check.py exit 1 with documented noise-class metrics per the audit-cma lineage envelope (baseline pristine, 8th consecutive audit-grade observation). Milestone 24 closes structurally; only the audit pipeline remains.

Per-task notes

• iter 24.3.1: Appended fn print to examples/prelude.ail.json after fn ge (last def pre-edit). 20 defs total (was 19). Body is the literal Term::Let { name: "s", value: App(show, [x]), body: Do(io/print_str, [s]) } with the constraint Show a bare per mq.1 same-module canonical form. 552 tests stay green.
• iter 24.3.2: crates/ail/tests/print_mono_body_shape.rs asserts post-mono print__Int.body shape. Initial test asserted outer Term::Lam wrapper — corrected after the panic surfaced that FnDef.body: Term is the inner function body for top-level fns (params carried separately on FnDef.params). The test now asserts directly Term::Let → App(show__Int, [x]) → Do(io/print_str, [s]), faithful to the plan's intent (preserve the explicit-let-binder discipline) while matching the actual AST shape.
• iter 24.3.3: examples/show_print_smoke.ail.json written with nested Term::Seq of four App(print, [lit]) calls (Int 42, Bool true, Str "hello", Float bits=40091eb851eb851f for 3.14). ail build clean; stdout: 42\ntrue\nhello\n3.14 — io/print_str appends a newline via @puts.
• iter 24.3.4: examples/show_user_adt.ail.json written + 2-test crates/ail/tests/show_print_e2e.rs. Surfaced three substantive plan-defects-fixed-inline (Concerns below); after fix, both E2E tests pass (print (MkIntBox 7) → stdout "7").
• iter 24.3.5: Extended NoInstance Float-aware arm in crates/ailang-check/src/lib.rs:770-779 with a parallel class == "prelude.Show" branch. The arm fires for ANY type lacking a Show instance (function types, user types without instance) — cross-references DESIGN.md §"Prelude (built-in) classes" verbatim. Negative fixture examples/show_no_instance.ail.json (let-bound f : Int -> Int + print f) and pin test in crates/ail/tests/show_no_instance_e2e.rs (asserts code, Show-substring, Prelude-(built-in)-classes substring). After the constraint-residual-push fix in synth (Concerns below), the diagnostic fires at typecheck.
• iter 24.3.6: DESIGN.md §"Prelude (built-in) classes" milestone-24 paragraph amended: print flipped to past tense ("shipped in iter 24.3"), body shape + pin file reference added, retirement follow-up named. DESIGN.md §"Float semantics" gained a new paragraph in the "Unspecified" block cross-referencing show 1.5 / show nan / show inf to instance Show Float via float_to_str. ~10 lines added net (2697 → 2707).
• iter 24.3.7: Roadmap P1 "Post-22 Prelude — Show + print rewire" entry flipped to [x] with a closing-summary block naming all three shipped iters (24.1 f38bad8, 24.2 iter-24.2, 24.3 this iter). New P2 entry "Retire io/print_int|bool|float effect-ops
  • migrate example corpus to print" inserted at top of P2, before the existing operator-routing-through-Eq/Ord entry.
• iter 24.3.8: Full workspace 556 passed / 0 failed. prelude_free_fns 5/5 green; mono_hash_stability 2/2 green (Eq/Ord hashes unchanged, Show hashes from 24.2 unchanged). bench/cross_lang.py exit 0 (25/25 stable). bench/compile_check.py exit 1 with 1 noise-class regression on a check_ms.* metric (regressed metric identity migrates between runs — pattern consistent with the documented noise envelope per audit-cma lineage, 8th consecutive observation). bench/check.py exit 1 with 2 improvements beyond tolerance on latency.explicit_at_rc.* — same envelope, same conservative call. Baseline pristine.

Concerns

• Three plan-defects-fixed-inline surfaced during Task 4 (user-ADT E2E). All three are necessary repairs to make the spec's stated user-ADT trajectory (§"Data flow / print x at user type IntBox" lines 297-310) work end-to-end. The plan did not anticipate them because the test architecture envisioned (Tasks 3+4 sharing one test file) didn't actually exercise the cross-module mono synthesis before this iter; primitive-only smoke worked through the existing pipeline.
  • (a) Bare type-cons in MonoTarget::FreeFn::type_args. At mono target-collection (collect_mono_targets + collect_residuals_ordered free-fn arms), subst.apply(meta) returns the unification result in whatever qualification the caller-module's view used. For a user-defined type referenced from main (in show_user_adt), IntBox came out bare. The downstream synthesise_mono_fn_for_free_fn then substituted bare IntBox everywhere in the synthesised body, and Phase 3 rewrite of the synthesised body (run in PRELUDE caller-module context, where IntBox is not a known TypeDef) saw Type::Con{IntBox} that didn't normalise to the registry-keyed show_user_adt.IntBox. Lookup missed → no show__IntBox target scheduled → bare Var "show" persisted post-mono. Fix: mono.rs lines 685-696 + 1267-1278 normalise via env.workspace_registry.normalize_type_for_lookup(module_name, &resolved) before pushing the type into MonoTarget::FreeFn::type_args. Same invariant applies symmetric to the existing r_ty_norm = normalize_type_for_lookup(...) calls already in collect_mono_targets's class-method arm.
  • (b) Codegen cross-module references via import_map. Post fix-(a), the synthesised body now correctly references show_user_adt.show__cb5eb497 from inside prelude.print__cb5eb497. But prelude does not have show_user_adt in its import_map (prelude is the base; user modules import IT, not the other way around). Three codegen sites raised UnknownVar: resolve_top_level_fn:2200, lower_app cross-module arm:1981, synth_with_extras Var arm:2777. All three now fall back to a direct module_user_fns.contains_key(prefix) (or module_def_ail_types.contains_key(prefix)) lookup when the prefix isn't in the current module's import_map. This is the post-mono synthesised-body invariant: cross-module references in synthesised bodies may bypass the source template's imports (both ends were independently typechecked under their own module contexts before mono ran; the cross-module reference is created by mono, not by the source). Doc comments cross-reference all three sites.
  • (c) Poly-free-fn constraint residuals not pushed at synth. Pre-iter-24.3, the FreeFnCall arm at lib.rs:2820 had constraints: _ — declared constraints of the poly free fn were ignored. For all milestone-23 fixtures (ne/lt/le/gt/ge at primitive types), this was latent because every call site had a registry entry; the mono pass silently scheduled the corresponding eq__T/compare__T targets, and codegen succeeded. But for negative cases — print f where f : Int -> Int has no Show instance — the constraint never reached the typecheck-time NoInstance discharge (lib.rs:1880-1905). The build would emit a confusing post-mono unknown variable: show from codegen rather than the right typecheck-phase diagnostic. Fix: at lib.rs:2820+, walk Type::Forall.constraints at FreeFnCall sites, substitute the rigid vars with their fresh metavars, and push one ResidualConstraint per declared constraint. The discharge loop then fires the correct NoInstance with full diagnostic context (including the Show-aware addendum from Task 5). Pre-existing milestone-23 tests stay green because primitive-type Show/Eq/Ord registry entries discharge silently.
• bench/compile_check.py + check.py exit 1. Both report noise-class metrics (1 regression / 2 improvements respectively). Metric identity migrates between consecutive runs — pattern consistent with the documented latency.implicit_at_rc.* / check_ms.* noise envelope per audit-cma + audit-ms + audit-eob + audit-ct-tidy + audit-mq + iter-24.2 lineage. 8th consecutive observation. Baseline pristine per conservative-call convention.
• Plan deviation on Task 2 (IR-shape pin). The plan's test stub asserted Term::Lam { body: Term::Let { ... } } for print__Int. The actual FnDef.body: Term shape for top-level fns is the inner function body (params separate); no outer Term::Lam. The test was corrected to assert Term::Let { ... } directly. The load-bearing property (explicit let-binder for heap-Str RC discipline) is identical between the plan's intent and the shipped assertion; only the wrapper assumption changed. Doc comment in the test file explains the FnDef.body shape contract.

Known debt

• Milestone 24 closes structurally with this iter. The standard audit pipeline (architect drift review + bench regression attribution) runs next. The three plan-defects-fixed-inline above may merit architect commentary on whether the fix sites belong as permanent invariants or are themselves transitional. Specifically: fix (a) implies that MonoTarget::FreeFn::type_args carries CANONICAL types post-collection — this is a strengthening of the pre-iter invariant which was "subst.apply result"; future planner work that touches the mono pass should keep that strengthening visible.
• P2 entry "Retire io/print_int|bool|float effect-ops" is queued. The new entry's ~86 fixtures affected count is from a rough grep against do io/print_<T>; precise count + migration plan is the planner's job when the milestone opens.
• Negative-fixture coverage is single-shape. show_no_instance.ail.json uses f : Int -> Int. Other NoInstance shapes (user type without instance, print x where x : SomeUnsupportedClass) are not separately tested — the NoInstance arm fires for any non-prelude-Show type by construction, so the single fixture is structurally representative.

Files touched

Created (6):

• crates/ail/tests/print_mono_body_shape.rs
• crates/ail/tests/show_print_e2e.rs
• crates/ail/tests/show_no_instance_e2e.rs
• examples/show_print_smoke.ail.json
• examples/show_user_adt.ail.json
• examples/show_no_instance.ail.json

Modified (6):

• examples/prelude.ail.json (+1 def: fn print)
• crates/ailang-check/src/lib.rs (NoInstance Show-aware branch + FreeFnCall constraint-residual push)
• crates/ailang-check/src/mono.rs (FreeFn type_args canonical-form normalisation, 2 sites)
• crates/ailang-codegen/src/lib.rs (cross-module reference fallback for post-mono synthesised bodies, 3 sites: resolve_top_level_fn, lower_app's cross-module call arm, synth_with_extras's Var arm)
• docs/DESIGN.md (§"Prelude (built-in) classes" milestone-24 paragraph + §"Float semantics" Show-Float cross-reference)
• docs/roadmap.md (P1 Show+print → [x]; new P2 entry at top)

Stats

bench/orchestrator-stats/2026-05-13-iter-24.3.json