haskell: Phase 10 — Floating stub: pi, exp, log, sin, cos, ** (+6 tests, 37/37)

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

plans/haskell-completeness.md

@@ -165,7 +165,7 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 - [x] `Fractional` typeclass stub: `(/)`, `recip`, `fromRational`. _(/)
   already a binop; `recip x = 1 / x` and `fromRational x = x` registered as
   builtins in the post-prelude block._
-- [ ] `Floating` typeclass stub: `pi`, `exp`, `log`, `sin`, `cos`, `(**)`
+- [x] `Floating` typeclass stub: `pi`, `exp`, `log`, `sin`, `cos`, `(**)`
   (power operator, maps to SX exponentiation).
 - [ ] Tests in `lib/haskell/tests/numeric.sx` (≥ 15 tests: fromIntegral
   identity, sqrt/floor/ceiling/round on known values, Float literal show,
@@ -303,6 +303,12 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Phase 10 Floating stub (pi, exp, log, sin, cos, **):
+- pi as a number constant; exp/log/sin/cos as builtins thunking through to SX
+  primitives. `(**)` added as a binop case in `hk-binop` mapping to SX `pow`.
+  6 new tests in `numerics.sx` (now 37/37). `2 ** 10 = 1024`, `log (exp 5) = 5`,
+  `sin 0 = 0`, `cos 0 = 1`, `pi ≈ 3.14159`, `exp 0 = 1`.
+
 **2026-05-07** — Phase 10 Fractional stub (recip, fromRational):
 - `(/)` already a binop. Added `recip` and `fromRational` as builtins
   post-prelude. 3 new tests in `numerics.sx` (now 31/31).