[project @ 1997-09-03 23:32:31 by sof]

new regression test

ghc/tests/programs/jon_polycase/Foo.lhs

+{- 
+	Date: Wed, 3 Sep 1997 10:25:35 +0200 (MET DST)
+	From: Jon Mountjoy <jon@wins.uva.nl>
+
+Hello Bug Hunters,
+
+The following program (rather condensed as it comes from something
+much larger), crashes the compiler. I am using ghc-2.05 on a Solaris
+box, with one or two patches(including the WwLib one which Simon gave
+me, but this error occured before applying this patch).
+
+It seems to be some rather subtle dependency problem.  Compiling with
+-O solves the problem, compiling with ghc -c Foo.lhs should highlight
+it.  The error message is appended below the file.  What are the new
+"discarding polymorphic case" warnings about?
+
+If you change any line in reallyFlatten, the program compiles fine.  
+Likewise if you change the type of LinearCode to Int!
+
+-}
+
+> -- SNIP START
+
+> module Foo where
+
+> import Array
+> import Monad
+
+> reallyFlatten ::  Int -> Int -> Interpreter ()
+> reallyFlatten x t
+>  = do
+>     let f  = goo x
+>     out $ show x
+>     setIStatus (IFlattened f f)
+>     return ()
+
+> goo :: Int -> LinearCode
+> goo = \x -> listArray (0,1) []
+
+%---------------------------------------------------------------------
+
+> type LinearCode = Array Int Int
+
+> data InterpStatus = IFlattened !LinearCode !LinearCode 
+> data SM = SM { interpStatus :: InterpStatus }
+> initialState = SM { interpStatus = IFlattened undefined undefined }
+
+> newtype Interpreter a = RepInterp ((SM,Int) -> IO (Error ((SM,Int),a)))
+> getRepInterp (RepInterp a ) = a
+
+> instance Functor Interpreter where
+>  map f (RepInterp intp ) 
+>   = RepInterp (\s -> case intp s of
+>			 g -> g >>= \q -> 
+>		          case q of
+>			   Error mes  -> return $ Error mes
+>			   Ok (s',a') -> return $ Ok (s',f a'))
+
+> instance Monad Interpreter where
+>  return x = RepInterp (\s -> return (Ok (s,x)))
+>  (RepInterp intp) >>= g 
+>    = RepInterp(\s -> case intp s of
+>			p -> p >>= \q ->
+>		         case q of
+>			  Error mes  -> return $ Error mes
+>			  Ok (s',x') -> getRepInterp (g x') s' )
+
+> instance OutputMonad Interpreter where
+>  out s = RepInterp (\st -> putStr s >> 
+> 			     return (Ok (st,())))
+
+> updateSM :: (SM -> SM) -> Interpreter SM
+> updateSM f = RepInterp (\s@(sm,ty) -> return $ Ok ((f sm,ty), sm))
+
+> setIStatus :: InterpStatus -> Interpreter InterpStatus
+> setIStatus is = updateSM (\sm -> sm {interpStatus = is}) >>= 
+>                 return.interpStatus
+
+> data Error a = Ok a | Error String 
+>     
+> class Monad m => OutputMonad m  where   
+>   out      :: String -> m ()
+> instance OutputMonad IO where
+>  out s = catch (putStr s) (\_ ->  fail $userError "Oh MY")

ghc/tests/programs/jon_polycase/Makefile

+TOP = ../..
+include $(TOP)/mk/boilerplate.mk
+
+# The bug was delicate: only happens without -O
+SRC_HC_OPTS += -Onot
+
+# Just compiling Foo successfully is OK
+all :: Foo.o
+
+include $(TOP)/mk/target.mk
+