Test Trac #7837

1 files changed, 24 insertions, 0 deletions

diff --git a/testsuite/tests/indexed-types/should_compile/T7837.hs b/testsuite/tests/indexed-types/should_compile/T7837.hs
new file mode 100644
index 0000000000..45235f8065
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T7837.hs
@@ -0,0 +1,24 @@
+{-# 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)