replacement for popen

[Uwe Schmidt]

Simon Marlow wrote:

> If you really must use hGetContents, then the hack above is necessary:
> you have to force the output strings before waiting for the process to
> terminate.  This would be slightly cleaner:
> >        res  <- hGetContents outH
> >        errs <- hGetContents errH
> >        forkIO (evaluate (length res))
> >        forkIO (evaluate (length errs))
>
> which avoids blocking the main thread, but ensures that all the data
> gets pulled as it becomes available.

in

> forkIO(evaluate(length res)) 

the types do not match. evaluate has result IO Int
but forkIO expects IO ().

I tried

> forkIO(evaluate(length res) >> return ()) 

but this version again blocks.

uwe