On Sep 30, 2009, at 2:20 AM, Martin Hofmann wrote:
Thanks a lot.
You ought to be able to add a Control.Monad.CatchIO.catch clause to your interpreter to catch this kind of errors, if you want.
I forgot to mention that this didn't work for me either.
Thanks for the report!
You are welcome. If you come up with a work around or a fix, I would appreciate if you let me know.
Cheers,
Martin
Apologies for a very very very late follow-up on this thread (http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64013 ). It turns out that Control.Monad.CatchIO.catch was the right thing to use; you were probably bitten, just like me, by the fact that "eval" builds a thunk and returns it, but does not execute it. The following works fine for me: import Prelude hiding ( catch ) import Language.Haskell.Interpreter import Control.Monad.CatchIO ( catch ) import Control.Exception.Extensible hiding ( catch ) main :: IO () main = print =<< (runInterpreter (code `catch` handler)) where s = "let lst [a] = a in lst []" code = do setImports ["Prelude"] forceM $ eval s handler (PatternMatchFail _) = return "catched!" forceM :: Monad m => m a -> m a forceM a = a >>= (\x -> return $! x) When run, it prints 'Right "catched!"'. Notice that if you change the line 'forceM $ eval s' by an 'eval s', then the offending thunk is reduced by the print statement and the exception is thrown outside the catch. Hope this helps Daniel