[project @ 2005-03-07 17:12:05 by simonpj]

Test recursive dictionaries

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

@@ -37,6 +37,8 @@ test('tcrun028', expect_fail_for(['extcore','optextcore']), compile_and_run, [''
 test('tcrun029', normal, compile_and_run, [''])
 test('tcrun030', normal, compile_and_run, [''])
 test('tcrun031', only_compiler_types(['ghc']), compile_and_run, [''])
+test('tcrun032', only_compiler_types(['ghc']), compile_and_run, [''])
+test('tcrun033', only_compiler_types(['ghc']), compile_and_run, [''])
 
 test('church', normal, compile_and_run, [''])
 test('testeq2', normal, compile_and_run, [''])

testsuite/tests/ghc-regress/typecheck/should_run/tcrun032.hs

+{-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
+
+-- This tests the recursive-dictionary stuff.
+--
+-- The derived instance needs 
+
+module Main where
+
+data Fix f = In (f (Fix f))  deriving( Show, Eq )
+data L x = Nil | Cons Int x  deriving (Show, Eq)
+
+main = do { print (In Nil); 
+	    print (In Nil == In Nil) }
+

testsuite/tests/ghc-regress/typecheck/should_run/tcrun032.stdout

+In Nil
+True

testsuite/tests/ghc-regress/typecheck/should_run/tcrun033.hs

+{-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
+
+-- This test made GHC 6.3 build a superclass loop, in
+-- the instance ClassA a String declaration
+
+module Main where
+
+class (Sat (a -> b -> String), ClassB b) => ClassA a b
+
+class ClassB a where
+  fun :: a -> String
+
+class Sat x where
+   sat :: x
+
+instance ClassA a b => Sat (a -> b -> String) where
+  sat = const fun
+
+instance ClassA a String
+-- Badness was that the ClassB superclass dict was loopy
+--
+-- Needs Sat (a -> String -> String), ClassB String
+-- --> ClassA a String, ClassB String
+-- and adding ClassA gives superclass ClassB.
+
+instance ClassB String where
+  fun = id
+
+main = print ((sat :: Int -> String -> String) 3 "hello")

testsuite/tests/ghc-regress/typecheck/should_run/tcrun033.stdout

+"hello"