Brummel
1fb225ee25
When `synth` visits a `Term::Var v` where v is a polymorphic free fn whose `Type::Forall` carries class constraints (e.g. `print : forall a. Show a => ...`, `lt`/`le`/`gt`/`ge : forall a. Ord a => ...`), it pushes BOTH a class `ResidualConstraint` for each constraint AND a `FreeFnCall` observation at the same Var site. The mono walkers (`interleave_slots` collection-side and `rewrite_mono_calls` rewrite-side) consumed only ONE slot per such Var, leaving the class-residual cursor misaligned for every subsequent class-method call in the same body. The next `eq`/`compare` Var in the body then consumed the leftover `Show T` / `Ord T` slot and was mis-rewritten — codegen reported `call prelude.show__Bool arg type mismatch: expected i1, got i64` (or the Int dual). Fix: new `poly_free_fn_constraint_counts_for_module` registry in mono.rs (sibling to `poly_free_fn_names_for_module`) maps each synth-visible poly-free-fn name to its declared constraint count. Threaded into `collect_residuals_ordered`, `interleave_slots`, and `rewrite_mono_calls`. Both walkers now advance the cursor by 1 + N (FreeFn slot + N class-residual fillers) at every poly-free-fn Var. RED test `print_with_class_method_arg_does_not_misalign_mono_cursor` (crates/ail/tests/show_print_e2e.rs) + fixture examples/print_eq_arg_repro.ail pin the bug — body `(app print (app eq 1 2))` previously crashed at codegen, now prints "false". Bug surfaced 2026-05-14 during the rpe.1 BLOCKED orchestrator run; existed in latent form since iter 24.3 (the poly-free-fn-with-class- constraint synth shape was new there). No schema / codegen / DESIGN.md changes. cargo test --workspace: 564 / 0 / 3.
96 lines
4.3 KiB
Markdown
96 lines
4.3 KiB
Markdown
# iter bugfix-mono-cursor-print-with-class-method-arg — `(app print (app eq …))` no longer rewrites the inner class-method to a stale `Show T` symbol
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**Date:** 2026-05-14
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**Started from:** 05e4c04e3ba74f3382216ff3ea285e3fb1e3a45d
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**Status:** DONE
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**Tasks completed:** 1 of 1
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## Summary
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The iter 24.3 `synth` Var-arm pushes BOTH a class `ResidualConstraint`
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for each declared constraint AND a `FreeFnCall` observation at the
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same poly-free-fn `Var` site (`crates/ailang-check/src/lib.rs` ≈ 2908–
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2966). The two mono walkers in `crates/ailang-check/src/mono.rs`,
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however, were each consuming exactly one slot per `Var`: at a
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poly-free-fn `Var` they popped one `free_fn_slot` and zero
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`class_slot`s. Every constraint on a poly-free-fn-with-constraints
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left a leftover class slot, so the next class-method `Var` in the
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same body consumed the wrong slot — the residual that belonged to
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`print`'s `Show T` constraint got cursor-aligned with the inner `eq`
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`Var`, and codegen reported `call prelude.show__Bool arg type
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mismatch: expected i1, got i64`.
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The fix advances both walkers' cursors by `1 + N` at a poly-free-fn
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`Var` whose source `Type::Forall` carries `N` class constraints. A
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new sibling helper `poly_free_fn_constraint_counts_for_module`
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mirrors `poly_free_fn_names_for_module`'s three-source spelling
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contract (same-module / implicit-import bare / dot-qualified
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`alias.name`) and produces a `BTreeMap<String, usize>` from synth-
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visible name to declared-constraint count. The map is threaded into
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the rewrite-phase loop alongside `poly_free_fns` and passed to both
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`rewrite_mono_calls` and `interleave_slots`.
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In `interleave_slots`, a poly-free-fn `Var` now pushes the `FreeFn`
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slot first (this is what the rewrite walker reads for the rename),
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then `N` filler entries drawn in order from `class_slots` (consumed
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only to keep `class_cur` aligned). In `rewrite_mono_calls`, the
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`Var`-arm captures `n_filler` from the count map BEFORE the rename
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mutates `name` (lookup keys are the synth-visible spelling), reads
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the slot at `*cursor` as before, then advances by `1 + n_filler`.
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Class-method `Var`s stay at advance-by-one (synth pushes exactly one
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residual and no `FreeFnCall`).
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## Per-task notes
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- task 1: write/verify the cursor-alignment fix.
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- Reproduced RED at `print_with_class_method_arg_does_not_misalign_mono_cursor`
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with the exact failure mode stated in the carrier:
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`call prelude.show__Bool arg type mismatch: expected i1, got i64`.
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- Added `poly_free_fn_constraint_counts_for_module` helper
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immediately after `poly_free_fn_names_for_module`; identical
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name-source contract, returning constraint counts instead of a
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presence set.
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- Threaded `poly_free_fn_ccounts: &BTreeMap<String, usize>` into
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`collect_residuals_ordered`, `interleave_slots`, and
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`rewrite_mono_calls` (signatures + every recursive call site).
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- `interleave_slots::Term::Var` poly-free-fn branch: after pushing
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the `FreeFn` slot, drain `N` entries from `class_slots` and push
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them as fillers in `out`, advancing `class_cur` by `N`.
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- `rewrite_mono_calls::Term::Var`: compute `n_filler` from the
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count map before the rename mutation, then `*cursor += 1 +
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n_filler`. Class-method `Var`s are guarded with `if
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is_poly_free_fn { … } else { 0 }`.
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- RED `print_with_class_method_arg_does_not_misalign_mono_cursor`
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flips to GREEN with stdout `false` as predicted by the fixture
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docstring.
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- Full `cargo test --workspace` passes 564 / 564 (= 563 baseline
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from `clippy-sweep` + the 1 new mini-mode RED). Zero
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regressions across any of the existing show / mono / typeclass
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test suites.
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## Concerns
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(none)
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## Known debt
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(none — the constraint set is a single new sibling helper plus a
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new threaded argument; the two-walker symmetry remains the invariant
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the existing comments already document.)
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## Files touched
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- `crates/ailang-check/src/mono.rs` — the fix (helper + two walker
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signatures + Var-arm cursor advancement + recursive-call
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threading).
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- `crates/ail/tests/show_print_e2e.rs` — RED pin
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`print_with_class_method_arg_does_not_misalign_mono_cursor`
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(committed by `/debug` upstream of this iter; flips RED → GREEN
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here).
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- `examples/print_eq_arg_repro.ail` — RED fixture (committed by
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`/debug` upstream; consumed by the pin).
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## Stats
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bench/orchestrator-stats/2026-05-14-iter-bugfix-mono-cursor-print-with-class-method-arg.json
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