On Tue, 2008-04-22 at 16:09 -0700, Don Stewart wrote:
duncan.coutts:
readProcess :: FilePath -- ^ command to run -> [String] -- ^ any arguments -> String -- ^ standard input -> IO (Either (ExitCode,String) String) -- ^ either the stdout, or an exitcode and any output
You don't need the Either. ExitCode already covers the case when the process terminates successfully.
But we want to force people to check the failure case. Just returning the tuple doesn't help there.
In Cabal we have two versions: usualConvenientVersion :: FilePath -> [String] -> IO String moreGeneralVersion :: FilePath -> [String] -> IO (String, ExitCode) The first version - that we expect to use most often - just throws an exception if the exit code is non-0. In our experience this is almost always the right thing to do. There is only one place in Cabal where we expect the command to fail but we need the output anyway. We previously had all our process functions return an ExitCode and they were routinely ignored. I suppose the fact that with readProcess people will be interested in the result does help the situation. Duncan