1 files changed, 31 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_compile/LoopOfTheDay1.hs b/testsuite/tests/typecheck/should_compile/LoopOfTheDay1.hs
new file mode 100644
index 0000000000..e3b656a66e
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/LoopOfTheDay1.hs
@@ -0,0 +1,31 @@
+{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, UndecidableInstances #-}
+
+-- Compiles fine.
+-- Instance selection works fine.
+-- try: :t foo (T1b T1a)
+
+module ShouldCompile where
+
+-- Notice: T1 is a recursive type.
+-- Notice: the classes are recursive, too.
+-- Why does this work when almost the same thing doesn't?
+-- Say: adding an Int component to T1a makes things loop.
+-- See LoopOfTheDay2.hs and LoopOfTheDay3.hs.
+
+data T1 = T1a | T1b T1
+
+class C0 x where foo :: x -> (); foo = undefined
+class C1 x y
+class C1 x y => C2 x y
+
+instance C0 T1              => C1 () T1		-- (I1)
+instance (C1 x T1)          => C2 x T1		-- (I2)
+instance C2 () T1           => C0 T1		-- (I3)
+
+baz = foo (T1b T1a)
+
+{- Need 	C0 T1
+-->(I3)		C2 () T1
+-->(I2)		C1 () T1
+-->(I1)		C0 T1		-- STOP because we've seen this before
+-}