David Roundy wrote:
On Wed, Apr 23, 2008 at 11:29:42AM -0700, Simon Marlow wrote:
So now we have:
Prelude System.Process> readProcessMayFail "ls" ["/foo"] "" (ExitFailure 2,"ls: /foo: No such file or directory\n") Prelude System.Process> readProcess "ls" ["/foo"] "" *** Exception: readProcess: ls: failed
Look ok?
Looks fine as an API. As an implementation, I'd prefer for the exception thrown to include stderr (and wouldn't mind if the output didn't include stderr). It'd be much nicer if we had:
Prelude System.Process> readProcess "ls" ["/foo"] "" *** Exception: readProcess: ls /foo: No such file or directory
This would mean that correct programs could use readProcess without sacrificing nice feedback when something unusual happens. Of course, we can't guarantee that stderr will give any hint as to what went wrong, but that's not our bug. We could also potentially include both stdout and stderr, or just the last few lines of the stdout/stderr combination.
Yes, there are a couple of problems here: 1. stdout and stderr are tied together, so we don't know which parts of the output are stderr. 2. the output might be multi-line, and it's not clear how much or which parts to include. The easy answer is just "include it all", but then the error messages could get arbitrarily long and potentially include a lot of superfluous information. However, I can certainly include the arguments and the exit code in the exception, which I'm not currently doing. Cheers, Simon