haskell: Phase 13 — Num default verification (negate/abs) (+3 tests, 13/13)

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

lib/haskell/tests/class-defaults.sx

@@ -64,4 +64,23 @@
   (hk-deep-force (hk-run (str hk-myord-source "main = myMax 4 4\n")))
   4)
 
+(define
+  hk-mynum-source
+  "class MyNum a where\n  mySub :: a -> a -> a\n  myLt :: a -> a -> Bool\n  myNegate :: a -> a\n  myAbs :: a -> a\n  myNegate x = mySub (mySub x x) x\n  myAbs x = if myLt x (mySub x x) then myNegate x else x\ninstance MyNum Int where\n  mySub x y = x - y\n  myLt x y = x < y\n")
+
+(hk-test
+  "Num default: myNegate 5 = -5"
+  (hk-deep-force (hk-run (str hk-mynum-source "main = myNegate 5\n")))
+  -5)
+
+(hk-test
+  "Num default: myAbs (myNegate 7) = 7"
+  (hk-deep-force (hk-run (str hk-mynum-source "main = myAbs (myNegate 7)\n")))
+  7)
+
+(hk-test
+  "Num default: myAbs 9 = 9"
+  (hk-deep-force (hk-run (str hk-mynum-source "main = myAbs 9\n")))
+  9)
+
 {:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}