crash caused by generic visitor (?)

[Simon Peyton-Jones]

Great, thanks. I've added that link to the user-documentation page for the GHC API, here
	http://haskell.org/haskellwiki/GHC/As_a_library#Links

Please do elaborate that page, which is a bit thin at the moment.  It should be easier to find supporting info about the GHC API.

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-users-
| bounces at haskell.org] On Behalf Of Ranjit Jhala
| Sent: 14 May 2011 17:52
| To: ghc-users
| Subject: Re: crash caused by generic visitor (?)
| 
| Hi all,
| 
| my apologies. Looks like the issue (and a fix!) is described here
| 
|   http://mistuke.wordpress.com/category/vsx/
| 
| Thanks,
| 
| Ranjit.
| 
| On May 13, 2011, at 4:34 PM, Ranjit Jhala wrote:
| 
| > Hi all,
| >
| > I'm trying to extract the set of identifiers that are read in given
| > source file.  To this end, I wrote the following code (full source at end.)
| >
| > ------------------------------------------------------------------------
| > main
| >  = do fname   <- (!! 0) `fmap` getArgs
| >       tcm     <- loadTypecheckedSource fname
| >       putStrLn $ showPpr tcm           -- this works fine
| >       putStrLn $ showPpr $ allIds tcm  -- this causes the crash
| >       return ()
| >
| > allIds ::  Data a => a -> [Id]
| > allIds = listify (\x -> case (x :: Id) of _ -> True)
| > ------------------------------------------------------------------------
| >
| > and where:
| >
| > 	loadTypecheckedSource ::  FilePath -> IO TypecheckedSource
| >
| > unfortunately, when I compile and run it, I get the dreaded:
| >
| > 	Bug: Bug: panic! (the 'impossible' happened)
| >  	(GHC version 7.0.3 for i386-unknown-linux):
| > 		placeHolderNames
| >
| > 	Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
| >
| > Turns out that the problem is when the file contains a type annotation.
| > That is,
| >
| > 	./Bug Test00.hs
| >
| > crashes, when Test00.hs is:
| >
| > 	module Test where
| >
| > 	x :: Int
| > 	x = 0
| >
| > but does not crash when the file is:
| >
| > 	module Test where
| >
| > 	x = 0
| >
| > Can anyone tell me why listify chokes in the latter case? (And how one might
| > get around the problem?) I include the full source below (compiled with: ghc --make
| Bug, using ghc 7.0.3)
| >
| > Thanks!
| >
| > Ranjit.
| >
| > -----------------------------------------------------------------------------------
| -------------------
| > import GHC
| > import Outputable
| > import DynFlags (defaultDynFlags)
| > import GHC.Paths (libdir)
| >
| > import System.Environment (getArgs)
| > import Control.Monad
| > import qualified Data.List as L
| > import Data.Data
| > import Data.Generics.Schemes (listify)
| >
| > main
| >  = do fname   <- (!! 0) `fmap` getArgs
| >       tcm     <- loadTypecheckedSource fname
| >       putStrLn $ showPpr tcm           -- this works fine
| >       putStrLn $ showPpr $ allIds tcm  -- this causes the crash
| >       return ()
| >
| > allIds ::  Data a => a -> [Id]
| > allIds = listify (\x -> case (x :: Id) of _ -> True)
| >
| > loadTypecheckedSource ::  FilePath -> IO TypecheckedSource
| > loadTypecheckedSource fname
| >  = defaultErrorHandler defaultDynFlags $
| >      runGhc (Just libdir) $ do
| >        df  <- getSessionDynFlags
| >        setSessionDynFlags df
| >        tgt <- guessTarget fname Nothing
| >        setTargets [tgt]
| >        load LoadAllTargets
| >        res <- load LoadAllTargets
| >        if failed res
| >          then pprPanic "Load Failed!!" (text "AAARGH!")
| >          else tm_typechecked_source `fmap` getTypecheckedModule fname
| >
| > findModSummary ::  GhcMonad m => FilePath -> m ModSummary
| > findModSummary fname
| >  = do msums <- depanal [] False
| >       case L.find ((fname ==) . ms_hspp_file) msums of
| >         Just msum -> return msum
| >         Nothing   -> pprPanic "ModuleName Lookup Failed!!" (text "AARGHC!")
| >
| > getTypecheckedModule :: GhcMonad m => FilePath -> m TypecheckedModule
| > getTypecheckedModule = findModSummary >=> parseModule >=> typecheckModule
| >
| >
| >
| 
| 
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