Test #13938, with expect_broken

test case: dependent/should_compile/T13938

2 files changed, 81 insertions, 0 deletions

diff --git a/testsuite/tests/dependent/should_compile/T13938.hs b/testsuite/tests/dependent/should_compile/T13938.hs
new file mode 100644
index 0000000000..3ba9e273e4
--- /dev/null
+++ b/testsuite/tests/dependent/should_compile/T13938.hs
@@ -0,0 +1,80 @@
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeInType #-}
+{-# LANGUAGE TypeOperators #-}
+module T13938 where
+
+import Data.Kind (Type)
+
+data family Sing (a :: k)
+data instance Sing (z :: [a]) where
+  SNil  :: Sing '[]
+  SCons :: Sing x -> Sing xs -> Sing (x:xs)
+
+data TyFun :: Type -> Type -> Type
+type a ~> b = TyFun a b -> Type
+infixr 0 ~>
+
+type family Apply (f :: k1 ~> k2) (x :: k1) :: k2
+type a @@ b = Apply a b
+infixl 9 @@
+
+data FunArrow = (:->) -- ^ '(->)'
+              | (:~>) -- ^ '(~>)'
+
+class FunType (arr :: FunArrow) where
+  type Fun (k1 :: Type) arr (k2 :: Type) :: Type
+
+class FunType arr => AppType (arr :: FunArrow) where
+  type App k1 arr k2 (f :: Fun k1 arr k2) (x :: k1) :: k2
+
+type FunApp arr = (FunType arr, AppType arr)
+
+instance FunType (:->) where
+  type Fun k1 (:->) k2 = k1 -> k2
+
+$(return []) -- This is only necessary for GHC 8.0 -- GHC 8.2 is smarter
+
+instance AppType (:->) where
+  type App k1 (:->) k2 (f :: k1 -> k2) x = f x
+
+instance FunType (:~>) where
+  type Fun k1 (:~>) k2 = k1 ~> k2
+
+$(return [])
+
+instance AppType (:~>) where
+  type App k1 (:~>) k2 (f :: k1 ~> k2) x = f @@ x
+
+infixr 0 -?>
+type (-?>) (k1 :: Type) (k2 :: Type) (arr :: FunArrow) = Fun k1 arr k2
+
+elimList :: forall (a :: Type) (p :: [a] -> Type) (l :: [a]).
+            Sing l
+         -> p '[]
+         -> (forall (x :: a) (xs :: [a]). Sing x -> Sing xs -> p xs -> p (x:xs))
+         -> p l
+elimList = elimListPoly @(:->)
+
+elimListTyFun :: forall (a :: Type) (p :: [a] ~> Type) (l :: [a]).
+                 Sing l
+              -> p @@ '[]
+              -> (forall (x :: a) (xs :: [a]). Sing x -> Sing xs -> p @@ xs -> p @@ (x:xs))
+              -> p @@ l
+elimListTyFun = elimListPoly @(:~>) @_ @p
+
+elimListPoly :: forall (arr :: FunArrow) (a :: Type) (p :: ([a] -?> Type) arr) (l :: [a]).
+                FunApp arr
+             => Sing l
+             -> App [a] arr Type p '[]
+             -> (forall (x :: a) (xs :: [a]). Sing x -> Sing xs -> App [a] arr Type p xs -> App [a] arr Type p (x:xs))
+             -> App [a] arr Type p l
+elimListPoly SNil                      pNil _     = pNil
+elimListPoly (SCons x (xs :: Sing xs)) pNil pCons = pCons x xs (elimListPoly @arr @a @p @xs xs pNil pCons)
diff --git a/testsuite/tests/dependent/should_compile/all.T b/testsuite/tests/dependent/should_compile/all.T
index bb21df7db1..684602cc94 100644
--- a/testsuite/tests/dependent/should_compile/all.T
+++ b/testsuite/tests/dependent/should_compile/all.T
@@ -28,3 +28,4 @@ test('T12176', normal, compile, [''])
 test('T14038', expect_broken(14038), compile, [''])
 test('T12742', normal, compile, [''])
 test('T13910', expect_broken(13910), compile, [''])
+test('T13938', expect_broken(13938), compile, [''])