1 files changed, 38 insertions, 0 deletions
diff --git a/testsuite/tests/indexed-types/should_compile/NonLinearLHS.hs b/testsuite/tests/indexed-types/should_compile/NonLinearLHS.hs
new file mode 100644
index 0000000000..dc0ae5392a
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+++ b/testsuite/tests/indexed-types/should_compile/NonLinearLHS.hs
@@ -0,0 +1,38 @@
+{-# LANGUAGE TypeFamilies, EmptyDataDecls, FlexibleContexts #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances, OverlappingInstances, UndecidableInstances #-}
+
+module NonLinearLHS where
+
+type family E a b
+type instance E a a = [a]
+
+foo :: E [Int] (E Int Int) -> Int
+foo = sum . concat
+
+data family F a b
+data instance F a a = MkF [a] 
+
+goo :: F Int Int -> F Bool Bool
+goo (MkF xs) = MkF $ map odd xs
+
+
+-- HList-like type equality
+
+data True; data False;
+
+type family EqTy a b
+type instance EqTy a a = True
+
+class EqTyP a b result
+instance (EqTy a b ~ isEq, Proxy isEq result) => EqTyP a b result
+
+class Proxy inp out
+instance (result ~ True) => Proxy True result
+instance (result ~ False) => Proxy notTrue result
+
+testTrue :: EqTyP Int Int r => r
+testTrue = undefined
+
+testFalse :: EqTyP Int Bool r => r
+testFalse = undefined
+\ No newline at end of file