haskell: fix string ↔ [Char] equality — palindrome 12/12, conformance 34/34 (269/269)

Haskell strings are [Char]. Calling reverse / head / length on a SX raw
string transparently produces a cons-list of char codes (via hk-str-head /
hk-str-tail in runtime.sx), but (==) then compared the original raw string
against the char-code cons-list and always returned False — so
"racecar" == reverse "racecar" was False.

Added hk-try-charlist-to-string and hk-normalize-for-eq in eval.sx; routed
== and /= through hk-normalize-for-eq so a string compares equal to any
cons-list whose elements are valid Unicode code points spelling the same
characters, and "[]" ↔ "".

palindrome.hs lifts from 9/12 → 12/12; conformance 33/34 → 34/34 programs,
266/269 → 269/269 tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/haskell/scoreboard.json

@@ -1,7 +1,7 @@
 {
   "date": "2026-05-07",
-  "total_pass": 266,
+  "total_pass": 269,
-  "total_fail": 3,
+  "total_fail": 0,
   "programs": {
     "fib": {"pass": 2, "fail": 0},
     "sieve": {"pass": 2, "fail": 0},
@@ -9,7 +9,7 @@
     "nqueens": {"pass": 2, "fail": 0},
     "calculator": {"pass": 5, "fail": 0},
     "collatz": {"pass": 11, "fail": 0},
-    "palindrome": {"pass": 9, "fail": 3},
+    "palindrome": {"pass": 12, "fail": 0},
     "maybe": {"pass": 12, "fail": 0},
     "fizzbuzz": {"pass": 12, "fail": 0},
     "anagram": {"pass": 9, "fail": 0},

lib/haskell/scoreboard.md

@@ -10,7 +10,7 @@ Updated 2026-05-07 · Phase 6 (prelude extras + 18 programs)
 | nqueens.hs | 2/2 | ✓ |
 | calculator.hs | 5/5 | ✓ |
 | collatz.hs | 11/11 | ✓ |
-| palindrome.hs | 9/12 | ✗ |
+| palindrome.hs | 12/12 | ✓ |
 | maybe.hs | 12/12 | ✓ |
 | fizzbuzz.hs | 12/12 | ✓ |
 | anagram.hs | 9/9 | ✓ |
@@ -38,4 +38,4 @@ Updated 2026-05-07 · Phase 6 (prelude extras + 18 programs)
 | config.hs | 10/10 | ✓ |
 | counter.hs | 7/7 | ✓ |
 | accumulate.hs | 8/8 | ✓ |
-| **Total** | **266/269** | **33/34 programs** |
+| **Total** | **269/269** | **34/34 programs** |

plans/haskell-completeness.md

@@ -315,6 +315,15 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Fix string ↔ `[Char]` equality. `reverse`/`length`/`head`/etc.
+on a string transparently coerce to a cons-list of char codes via `hk-str-head`
++ `hk-str-tail`, but `(==)` then compared the original raw string against the
+char-code cons-list and always returned False. Added `hk-try-charlist-to-string`
++ `hk-normalize-for-eq` in `eval.sx` and routed `==` / `/=` through them, so a
+string compares equal to any cons-list whose elements are valid Unicode code
+points spelling the same characters (and `[]` ↔ `""`). palindrome.hs now 12/12;
+conformance lifts to 34/34 programs, **269/269 tests** — full green.
+
 **2026-05-07** — Phase 15 IORef complete (5 ops + module wiring + 13 unit
 tests + 2 conformance programs). `hk-bind-data-ioref!` in `eval.sx` registers
 `newIORef`, `readIORef`, `writeIORef`, `modifyIORef`, `modifyIORef'` under the