Hi all, A program that I built with GHC is crashing at runtime with the following error: internal error: eval_thunk_selector: strange selectee 12 I have not found much via Google, just an old post regarding ghc 6.0 that recommends cleaning and rebuilding. I have cleaned the build directory and re-built the executable, and I still get the error. The program is a compiler, and this error began showing up after I added support for memoization of results using the ST Monad and STRefs. For example, the following function creates a reference to a thunk: newMutableRef m = do ref <- newSTRef $ error "access ref too soon!" let m' = do r <- m writeSTRef ref (return r) return r writeSTRef ref m' return $ ref Here's some information about my system: - GHC 6.12.1 - Mac OS X 10.6.3 (Snow Leopard) So, what could cause this error? Any suggestions that can help me narrow down the problem would be greatly appreciated. If this is in fact a GHC bug, I'd like to find a workaround for now and also reproduce it in a small example so I can file a bug report. - Philip