haskell: Phase 8 — tests/show.sx expanded to 26/26 (full audit coverage)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plans/haskell-completeness.md

@@ -110,9 +110,11 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 - [x] `showsPrec` / `showParen` stubs so hand-written Show instances compile.
 - [x] `Read` class stub — just enough for `reads :: String -> [(a,String)]` to
   type-check; no real parser needed yet.
-- [ ] Tests in `lib/haskell/tests/show.sx` (≥ 12 tests: show Int, show Bool,
+- [x] Tests in `lib/haskell/tests/show.sx` (≥ 12 tests: show Int, show Bool,
   show Char, show String, show list, show tuple, show Maybe, show custom ADT,
   deriving Show on multi-constructor type, nested constructor parens).
+  _Char tests deferred: Char = Int representation; show on a Char is currently
+  `"97"` not `"'a'"`._
 - [ ] Conformance programs:
   - `showadt.hs` — `data Expr = Lit Int | Add Expr Expr | Mul Expr Expr`
     with `deriving Show`; prints a tree.
@@ -287,6 +289,16 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Phase 8 `tests/show.sx` expanded to full audit coverage (26/26):
+- 16 new direct `show` tests: Int (positive + negative), Bool (T/F), String,
+  list of Int, empty list, pair tuple, triple tuple, Maybe Nothing, Maybe Just,
+  nested Just (paren wrapping), Just (negate 3) (negative wrapping), nullary
+  ADT, multi-constructor ADT with args, list of Maybe.
+- `show ([] :: [Int])` would be the natural empty-list test but our parser
+  doesn't yet support type ascription; used `show (drop 5 [1,2,3])` instead.
+  Char `'a'` → `"'a'"` deferred to Char-tagging design (Char = Int currently
+  yields `"97"`).
+
 **2026-05-07** — Phase 8 `Read` class stub (`reads`, `readsPrec`, `read`):
 - Three lines added to `hk-prelude-src`: `reads s = []`, `readsPrec _ s = reads s`,
   `read s = fst (head (reads s))`. The stubs let user code that mentions