[project @ 2005-12-16 14:56:50 by simonpj]

Add repeated-type-variable tests for instance constexts

testsuite/tests/ghc-regress/typecheck/should_fail/all.T

@@ -138,3 +138,4 @@ test('tcfail150', normal, compile_fail, [''])
 test('tcfail151', normal, compile_fail, [''])
 test('tcfail152', normal, compile_fail, [''])
 test('tcfail153', normal, compile_fail, [''])
+test('tcfail154', normal, compile_fail, [''])

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail154.hs

+{-# OPTIONS -fglasgow-exts #-}
+
+module ShouldFail where
+
+data T a = MkT
+
+class C a b where
+  op :: T a -> T b -> Bool
+
+-- Repeated type variable in an instance constraint
+-- should require -fallow-undecidable-instances
+instance C a a => Eq (T a) where
+  (==) = op

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail154.stderr

+
+tcfail154.hs:12:0:
+    Non-type variables, or repeated type variables,
+      in the constraint: C a a
+    (Use -fallow-undecidable-instances to permit this)
+    In the context: (C a a)
+    While checking the context of an instance declaration
+    In the instance declaration for `Eq (T a)'