[project @ 1998-07-09 08:01:13 by sof]

Check if one method dict bug in 3.02 has been squashed

ghc/tests/typecheck/should_run/tcrun003.hs

+--!!! One method class from Sergey Mechveliani 
+--    showed up problematic newtype dict rep.
+module Main where
+import Ratio 
+
+class MBConvertible a b  where  cm :: a -> b -> Maybe b
+
+c :: MBConvertible a b => a -> b -> b
+c                         a    b =  case  cm a b  
+                                    of 
+                                      Just b' -> b'
+                                      _       -> error "c a b  failed"
+
+
+instance MBConvertible Int Int  where  cm a _ = Just a
+
+instance (MBConvertible a b,Integral b) => MBConvertible a (Ratio b)
+  where
+  cm a f =  case  cm a (numerator f)  of  Just a' -> Just (a'%1)
+                                          _       -> Nothing 
+  
+main =  let  f  = 1%1 :: Ratio Int
+             n2 = 2::Int
+             g  = (c n2 f) + f
+        in
+             putStr (shows g "\n")

ghc/tests/typecheck/should_run/tcrun003.stdout

+3 % 1