1 files changed, 36 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_compile/tc176.hs b/testsuite/tests/typecheck/should_compile/tc176.hs
new file mode 100644
index 0000000000..d05ccdbe29
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/tc176.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE FlexibleInstances, OverlappingInstances #-}
+
+{-  With "hugs -98 +o test.hs" gives me:
+    ERROR "test.hs":8 - Cannot justify constraints in instance member binding
+    *** Expression    : fromStr
+    *** Type          : FromStr [a] => String -> [a]
+    *** Given context : FromStr [a]
+    *** Constraints   : FromStr [a]
+
+    Adding the constraint "FromStr a" to the declaration of fromStr fixes 
+    the problem, but that seems like it should be redundant. Removing the 
+    second instance (lines 10-11) also fixes the problem, interestingly enough.
+
+    /Bjorn Bringert -}
+
+-- August 08: on reflection I think a complaint about overlapping
+-- instances for line 8 is absolutely right, so I've changed this to
+-- expected-failure
+
+-- Sept 08: on further reflection (!) I'm changing it back
+-- See Note [Subtle interaction of recursion and overlap]
+-- in TcInstDcls
+
+module ShouldCompile  where
+
+class FromStr a where
+     fromStr :: String -> a
+
+typeError :: FromStr a => a -> a
+typeError t = error "type error"
+
+instance FromStr [a] where
+     fromStr _ = typeError undefined  -- line 8
+
+instance FromStr [(String,a)] where  -- line 10
+     fromStr _ = typeError undefined  -- line 11