how to terminate an external program after timeout?

Hi, we call from our haskell application the metis prover via System.Process.readProcessWithExitCode "metis" filename "" However, we are not able to get rid of this process if metis does not terminate by itself. In particular, wrapping this call into a System.Timeout.timeout does not work. Any suggestions how we should handle this ideally portably but first of all under unix. (ghc-6.12.3) Thanks Christian