From 2f453414c5b1b27b6a84a3b5c7cd1bb5449f1f5d Mon Sep 17 00:00:00 2001
From: Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io>
Date: Thu, 7 Mar 2019 19:08:59 +0100
Subject: [PATCH] Add a test for Trac #13951
It no longer gives a warning.
---
.../tests/typecheck/should_compile/T13951.hs | 19 +++++++++++++++++++
.../tests/typecheck/should_compile/all.T | 1 +
2 files changed, 20 insertions(+)
create mode 100644 testsuite/tests/typecheck/should_compile/T13951.hs
diff --git a/testsuite/tests/typecheck/should_compile/T13951.hs b/testsuite/tests/typecheck/should_compile/T13951.hs
new file mode 100644
index 000000000000..8cbeb8c11ac5
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T13951.hs
@@ -0,0 +1,19 @@
+{-# LANGUAGE PolyKinds, GADTs, Rank2Types, ScopedTypeVariables, Trustworthy #-}
+module Control.Monad.Skeleton.Internal where
+
+data Cat k a b where
+ Empty :: Cat k a a
+ Leaf :: k a b -> Cat k a b
+ Tree :: Cat k a b -> Cat k b c -> Cat k a c
+
+viewL :: forall k a b r. Cat k a b
+ -> ((a ~ b) => r)
+ -> (forall x. k a x -> Cat k x b -> r)
+ -> r
+viewL Empty e _ = e
+viewL (Leaf k) _ r = k `r` Empty
+viewL (Tree a b) e r = go a b where
+ go :: Cat k a x -> Cat k x b -> r
+ go Empty t = viewL t e r
+ go (Leaf k) t = r k t
+ go (Tree c d) t = go c (Tree d t)
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index d312f5074dc1..b94f0210585e 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -669,3 +669,4 @@ test('T16188', normal, compile, [''])
test('T16204a', normal, compile, [''])
test('T16204b', normal, compile, [''])
test('T16225', normal, compile, [''])
+test('T13951', normal, compile, [''])
--
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