Re: [Haskell-cafe] Wrapping external process communication in a nice API?

Tristan Cacqueray writes:

On Mon, May 31, 2021 at 17:31 Mario Lang wrote:

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Tristan Cacqueray writes:

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It seems like it would be safer to use withCreateProcess instead of createProcess to ensure the process is not left unattended.

Maybe I am unimaginative, but it seems to me I can not use withCreateProcess as I need to read/write the Handles outside of the initialisation phase. It seems to me withCreateProcess would kill my external process once my initialisation function is done. Or do I misunderstand bracket somehow? AIUI, withCreateProcess always calls cleanupProcess once the action is done, right?

I guess you would have to replace `start'` with something like:

```haskell withEngine :: Time unit -> ... -> (Engine -> IO ()) -> IO () ```

And let your user provide the `Engine -> IO ()` callback.

Ahh, of course, push the problem up the caller chain :-) And I guess if that caller needs a sort of handle, it would do it with a channel to communicate with its action? I know I was asking for idiomatic code, and I am thankful for the pointer. Exception safety is clearly a good goal. But, I wonder, is limiting the API in such a way worth the trouble? It looks like this change would trigger a complete rewrite of the current module and all its clients. I'd like to be confident this is the right thing to do before doing that.

Alternatively, perhaps the `managed` library can be used to get something closer to your existing `start'`, e.g.: http://hackage.haskell.org/package/managed-1.0.8/docs/Control-Monad-Managed....

Ahh, thanks again. I'll have to digest all of this. -- CYa, ⡍⠁⠗⠊⠕