Add a test that apparently made the typechecker loop (around Feb 08)

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

@@ -189,6 +189,7 @@ test('tcfail197', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
 test('tcfail198', normal, compile_fail, [''])
 test('tcfail199', normal, compile_fail, [''])
 test('tcfail200', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
+test('tcfail201', normal, compile_fail, [''])
 
 test('T1899', normal, compile_fail, [''])
 test('T2126', normal, compile_fail, [''])

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail201.hs

+{-# OPTIONS_GHC -fglasgow-exts #-}
+
+
+-- Claus reported by email that 
+-- GHCi, version 6.9.20080217 loops on this program
+-- http://www.haskell.org/pipermail/cvs-ghc/2008-June/043173.html
+-- So I'm adding it to the test suite so that we'll see it if it happens again
+
+module Foo where
+
+data HsDoc id
+  = DocEmpty
+  | DocParagraph (HsDoc id)
+
+gfoldl' :: (forall a b . c (a -> b) -> a -> c b) -> (forall g . g -> c g) -> a -> c a
+gfoldl' k z hsDoc = case hsDoc of
+			  DocEmpty                  -> z DocEmpty
+			  (DocParagraph hsDoc)      -> z DocParagraph `k` hsDoc
+
+
+
+
+

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail201.stderr

+
+tcfail201.hs:17:5:
+    Couldn't match expected type `a' against inferred type `HsDoc id'
+      `a' is a rigid type variable bound by
+          the type signature for `gfoldl'' at tcfail201.hs:15:77
+    In the pattern: DocEmpty
+    In a case alternative: DocEmpty -> z DocEmpty
+    In the expression:
+        case hsDoc of
+          DocEmpty -> z DocEmpty
+          (DocParagraph hsDoc) -> z DocParagraph `k` hsDoc