Test Trac #7837

testsuite/tests/indexed-types/should_compile/T7837.hs

+{-# LANGUAGE TypeFamilies, FlexibleContexts #-}
+
+module T7837 where
+
+type family Scalar a
+class Fractional (Scalar a) => Norm a where
+  norm :: a -> Scalar a
+
+type instance Scalar Double = Double
+instance Norm Double where norm = abs
+
+normalize :: (Norm a, a ~ Scalar a) => a -> a
+normalize x = x / norm x
+{-# NOINLINE normalize #-}
+
+normalize_Double :: Double -> Double
+normalize_Double = signum
+{-# NOINLINE normalize_Double #-}
+
+-- This rule should fire in 'foo'
+{-# RULES "normalize/Double" normalize = normalize_Double #-}
+
+foo :: Double
+foo = normalize (4 :: Double)

testsuite/tests/indexed-types/should_compile/T7837.stderr

+Rule fired: Class op abs
+Rule fired: Class op signum
+Rule fired: normalize/Double

testsuite/tests/indexed-types/should_compile/all.T

@@ -209,4 +209,5 @@ test('T7489', normal, compile, [''])
 test('T7585', normal, compile, [''])
 test('T7282', normal, compile, [''])
 test('T7804', normal, compile, [''])
+test('T7837', normal, compile, ['-O -ddump-rule-firings'])