# iter 24.2 — Show class + 4 primitive instances + 22b TShow/tshow migration

**Date:** 2026-05-13
**Started from:** 64cea0e
**Status:** DONE
**Tasks completed:** 8 of 8

## Summary

Ships `class Show a where show : (a borrow) -> Str` in
`examples/prelude.ail.json` alongside primitive instances `Show Int`,
`Show Bool`, `Show Str`, `Show Float`. Each instance body is a
single-application lambda invoking the corresponding runtime primitive
(`int_to_str`, `bool_to_str`, `str_clone`, `float_to_str`) — first
prelude instance bodies to call runtime primitives directly
(prior Eq/Ord bodies used operator + codegen intercept). The 22b
typeclass test corpus migrates `class Show` / `show` →
`class TShow` / `tshow` preemptively (Tasks 1–2 before Task 3 lands
`prelude.Show`) so the workspace stays green throughout. Three new
tests pin the post-mono shape: mono-synthesis existence
(`show_mono_synthesis.rs`), dispatch singleton (`show_dispatch_pin.rs`
× 2 cases), and body-hash stability (`mono_hash_stability.rs::primitive_show_mono_symbol_hashes_stay_bit_identical`).
DESIGN.md §"Prelude (built-in) classes" gains a milestone-24 paragraph
naming Show + instances + the Float caveat. `print`-rewire stays
deferred to iter 24.3.

## Per-task notes

- iter 24.2.1: Renamed `"Show"`/`"show"` → `"TShow"`/`"tshow"` across 21
  `test_22b*_*.ail.json` fixture files; cross-module qualifier forms
  (`"<modname>.Show"` → `"<modname>.TShow"`) handled by regex in 3
  fixtures (`test_22b1_dup_a`, `test_22b1_dup_b`,
  `test_22b1_orphan_third`). False-positive scan empty; fixture
  parse round-trip green.
- iter 24.2.2: Renamed literals in `crates/ail/tests/typeclass_22b{2,3}.rs`
  (`"Show"` → `"TShow"`, `"show"` → `"tshow"`, `show__T` → `tshow__T`),
  including comment-prose forms (`` `Show` `` → `` `TShow` ``,
  `class Show` → `class TShow`, etc.) and one assertion-message string
  ("exactly one show__Int across the workspace" → "tshow__Int...").
  Plan undercount surfaced: the rename touches more than the 2 named
  test files — see Concerns below.
- iter 24.2.3: Inserted 5 new top-level defs into `examples/prelude.ail.json`
  immediately before `fn ne` (line 223 pre-edit). The `instance Show Str`
  body invokes `str_clone` as `Term::Var` — first prelude instance body
  to do so. Round-trip green; `primitive_eq_ord_mono_symbol_hashes_stay_bit_identical`
  stays green (Eq/Ord hashes unaffected by Show defs).
- iter 24.2.4: New fixture `examples/show_mono_pin_smoke.ail.json`
  exercises `show 42`, `show true`, `show "x"`, `show 1.5` in a
  let-chain ending in `io/print_str s1`. New test
  `crates/ail/tests/show_mono_synthesis.rs::primitive_show_mono_symbols_synthesise`
  asserts `show__Int`/`show__Bool`/`show__Str`/`show__Float` materialise
  as `Def::Fn` entries in the `prelude` post-mono module. `str_clone`
  reachability in instance-lambda position verified implicitly:
  `show__Str` materialises, which means the lambda body's `Term::Var
  "str_clone"` resolved against the checker's builtin table during
  typecheck.
- iter 24.2.5: New pin test `crates/ailang-check/tests/show_dispatch_pin.rs`
  asserts `env.method_to_candidate_classes["show"] == {"prelude.Show"}`
  (singleton) and `env.method_to_candidate_classes["tshow"] == {"*.TShow"}`
  (singleton). API spelled `build_check_env(&ws)` not `Env::from_workspace`
  (plan's placeholder name). 2/2 cases pass first-shot.
- iter 24.2.6: Extended `crates/ail/tests/mono_hash_stability.rs` with
  a second test function `primitive_show_mono_symbol_hashes_stay_bit_identical`
  loading `show_mono_pin_smoke.ail.json` (kept separate from the
  Eq/Ord fixture to avoid coupling). Hashes captured first-run:
  `show__Int 891eaebe64b3180d`, `show__Bool 1bdb621494e50607`,
  `show__Str 3f1d57c90ddce081`, `show__Float 5ab0bdd40b9f8b8f`.
- iter 24.2.7: DESIGN.md §"Prelude (built-in) classes" amended:
  milestone-23 paragraph drops "Show" from the deferred list and notes
  Show ships in milestone 24; new milestone-24 paragraph names class
  signature, instance set (including Float), body shape (single-app
  lambda invoking runtime primitive), and the iter-24.3 carry-forward
  for `print`-rewire.
- iter 24.2.8: Workspace tests 552 passed / 0 failed
  (was 548 pre-iter, +4 new: 1 `show_mono_synthesis` + 2 `show_dispatch_pin`
  + 1 hash-stability). `bench/compile_check.py` exit 0 (24/24 stable).
  `bench/cross_lang.py` exit 0 (25/25 stable). `bench/check.py` exit 1
  with 2 noise-class metrics (`bench_list_sum.bump_s` +11.71% — 4th
  consecutive sighting per `audit-mq` / `mq.tidy` lineage;
  `latency.implicit_at_rc.max_us` +145.55% — 7th consecutive sighting of
  the documented noise envelope, metric-identity-migrating across runs).
  Baseline pristine per the conservative-call convention.

## Concerns

- **Plan undercount on 22b migration scope.** The plan's "2 Rust test
  files" carrier (typeclass_22b{2,3}.rs) missed 4 additional consumer
  sites that hardcode the renamed literals: (a)
  `crates/ailang-core/src/hash.rs` ct4 canonical-form hash pin (2
  entries); (b) `crates/ailang-core/src/workspace.rs` 3 in-crate iter22b1
  tests; (c) `crates/ailang-prose/tests/snapshot.rs` (1 snapshot file at
  `examples/test_22b2_instance_present.prose.txt`); (d) one
  `mono_symbol_compound_type_uses_hash_suffix` assertion in typeclass_22b3.rs
  that called `mono_symbol("tshow", ...)` (post my batch rename) but
  still asserted `name.starts_with("show__")`. All fixed inline per the
  precedent of mq.1 / mq.3 "Plan defects fixed inline" — fixture parse
  was the only "green" pre-iter signal the plan's Step 3/4 anchored on,
  which masked the broader downstream consumer surface. Suggested
  Boss-side reaction: future migration plans run an upfront
  `grep -rln '"<rename target>"' crates/` to enumerate the full
  consumer set before committing to a per-file enumeration.
- **`str_clone` reachability is implicit.** Pre-flight note 3 flagged
  this as needing first-round-trip verification; verification is
  implicit in `primitive_show_mono_symbols_synthesise` passing
  (mono of `show 42 / true / "x" / 1.5` requires the four `show__T`
  bodies to typecheck, including the `str_clone` call in `show__Str`).
  No explicit isolated unit test for `str_clone`-in-lambda was added
  because the integration pin is strictly stronger; consider an
  isolated unit pin only if a future regression makes the integration
  test slow to bisect.
- **Hash-stability pin uses a separate fixture, not the existing
  `mono_hash_pin_smoke.ail.json`.** Plan Task 6 offered both options;
  the separate-fixture path was chosen because `show_mono_pin_smoke.ail.json`
  already existed (minted in Task 4) and reusing it kept the Eq/Ord
  pin structurally isolated. Both fixtures live side-by-side; the
  second test function in `mono_hash_stability.rs` mirrors the first
  byte-for-byte modulo the fixture path and pin table.
- **`bench/check.py` exit 1 is the documented recurring noise envelope.**
  `latency.implicit_at_rc.*` max-tail metric has been migrating
  between runs since `audit-cma` (2026-05-12) — 7th consecutive
  observation; `bench_list_sum.bump_s` is the 4th since `audit-mq`.
  Plan Task 8 Step 4 explicitly anticipates "1-3 regressed metrics
  ratify-without-attribution per conservative-call convention"; this
  iter follows that. The baseline stays pristine.

## Known debt

- **iter 24.3 still pending.** Carries `print : forall a. Show a => a -> () !IO`
  rewire to route through `show` + `io/print_str`. Spec at
  `docs/specs/2026-05-13-24-show-print.md`. 24.2 is structurally
  complete; 24.3 is operationally distinct.
- **mq1 cross-module fixtures unmigrated by design.**
  `examples/mq1_xmod_constraint_class.ail.json` and `..._dep.ail.json`
  reference `mq1_xmod_constraint_class_dep.Show` (cross-module, fully
  qualified) and ship zero `show` call sites; no dispatch ambiguity
  arises once `prelude.Show` lands. They stay as-is per the plan's
  pre-flight ratification.
- **mq3 fixtures deliberately retain two-Show shapes.**
  `examples/mq3_two_show_*` fixtures test the multi-class dispatch
  scenarios (ambiguity + qualifier resolution) and stay unchanged in
  24.2 by design.

## Files touched

**Created (3):**
- `crates/ail/tests/show_mono_synthesis.rs`
- `crates/ailang-check/tests/show_dispatch_pin.rs`
- `examples/show_mono_pin_smoke.ail.json`

**Modified (29):**

Prelude + DESIGN:
- `examples/prelude.ail.json` (+5 defs)
- `docs/DESIGN.md` (§"Prelude (built-in) classes" amendment)

22b fixture migration (21 files):
- `examples/test_22b1_dup_a.ail.json`
- `examples/test_22b1_dup_b.ail.json`
- `examples/test_22b1_dup_classmod.ail.json`
- `examples/test_22b1_dup_same_module.ail.json`
- `examples/test_22b1_orphan_class.ail.json`
- `examples/test_22b1_orphan_third.ail.json`
- `examples/test_22b1_orphan_third_classmod.ail.json`
- `examples/test_22b2_class_method_lookup.ail.json`
- `examples/test_22b2_constraint_declared.ail.json`
- `examples/test_22b2_instance_present.ail.json`
- `examples/test_22b2_missing_constraint.ail.json`
- `examples/test_22b2_no_instance.ail.json`
- `examples/test_22b2_two_fns_missing_constraint.ail.json`
- `examples/test_22b2_xmod_classmod.ail.json`
- `examples/test_22b2_xmod_classmod_noinst.ail.json`
- `examples/test_22b2_xmod_instance_present.ail.json`
- `examples/test_22b2_xmod_missing_constraint.ail.json`
- `examples/test_22b2_xmod_no_instance.ail.json`
- `examples/test_22b3_dup_call_sites.ail.json`
- `examples/test_22b3_no_call_sites.ail.json`
- `examples/test_22b3_shadow_class_method.ail.json`

22b consumer-test migration (5 source files + 1 snapshot):
- `crates/ail/tests/typeclass_22b2.rs`
- `crates/ail/tests/typeclass_22b3.rs`
- `crates/ailang-core/src/hash.rs` (ct4 hash pin)
- `crates/ailang-core/src/workspace.rs` (3 iter22b1 tests)
- `crates/ail/tests/mono_hash_stability.rs` (new show test fn)
- `examples/test_22b2_instance_present.prose.txt` (snapshot accept)

## Stats

`bench/orchestrator-stats/2026-05-13-iter-24.2.json`