1 files changed, 34 insertions, 0 deletions
diff --git a/testsuite/tests/cpranal/sigs/T2387.hs b/testsuite/tests/cpranal/sigs/T2387.hs
new file mode 100644
index 0000000000..71639dee19
--- /dev/null
+++ b/testsuite/tests/cpranal/sigs/T2387.hs
@@ -0,0 +1,34 @@
+{-# LANGUAGE TypeOperators, BangPatterns #-}
+
+module T2387 (mainLoop) where
+
+import Control.Monad.ST
+
+import System.Environment
+
+data (:*:) a b = !a :*: !b
+
+whileLoop :: Int -> ST s Int
+whileLoop = go 0
+ where
+ go !n k
+   | k == 0    = return n
+   | otherwise = go (n+1) (k-1)
+{-# INLINE whileLoop #-}
+
+iter :: Int -> Int -> ST s (Bool :*: Int)
+iter k n = do
+  k' <- whileLoop 40 >>= \k' -> return $! max k k'
+  b <- return (n == 0)
+
+  return $! b :*: k'
+{-# INLINE iter #-}
+
+-- | The returned Int should be unboxed
+mainLoop :: Int -> Int -> ST s Int
+mainLoop k n = do
+  done :*: k' <- iter k n
+
+  if done
+    then return k'
+    else mainLoop k' (n - 1)