Proposal: overhaul System.Process

Brian Brunswick brian.brunswick+haskell-libraries at
Fri May 16 10:44:37 EDT 2008

On Thu, May 15, 2008 at 10:45 AM, Simon Marlow <marlowsd at> wrote:
> The latest version of the Process overhaul is here:
>  - changes to readProcess, and added readProcessWithExitCode,
>    as discussed on the list.

I'd just like to argue briefly again against merging stdout and stderr.
My previous message didn't get to the whole list because of a different
from address to that I subscribed with.

* In other languages and cases in production code that has to deal with
errors in a nice way, I have always in the past wanted separate stdout
and stderr,
and never come across a case where they needed to be merged.

* Its not type safe! Surely the haskell spirit should not be to mix up two
streams of output, with fundamentally different meanings. Data goes to
stdout, errors and warnings go to stderr.

* Most unix utilities are designed for separation to make sense.

* The library should discourage careless programming that can mix
errors in with data.

Brian_Brunswick____brian at ithil.org____Wit____Disclaimer____!Shortsig_rules!

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