Discussion about libraries for Haskell

Evan Laforge | 8 Feb 22:25

documentation patch for process

I recently burned some time because I didn't realize that
System.Process.createProcess doesn't report when the binary isn't
found.  I guess I was used to that behaviour from python's subprocess
module, which goes to some effort to report the error from the
fork()ed child when exec() fails.  After a failed solution, I did some
poking around in the source to see exactly what haskell's process
does.

In the interests of saving someone else that time, I submit a patch to
process to add some documentation.  I'm not sure how to do a 'darcs
send' with git, but here's the patch:

% git log | head
commit 5a46937961b3400fa58ccffc785d0de8c1c01d94
Author: Evan Laforge <qdunkan <at> gmail.com>
Date:   Wed Feb 8 13:25:16 2012 -0800

    More detailed haddock for createProcess: document what happens if
    the binary is not found

commit c8b30a6f1d493ab724f2da05dbc49496b119a051
Author: Simon Marlow <marlowsd <at> gmail.com>
Date:   Mon Jan 16 16:25:34 2012 +0000

% git diff HEAD\^
diff --git a/System/Process.hs b/System/Process.hs
index f3a8f9b..a372228 100644
--- a/System/Process.hs
+++ b/System/Process.hs
@@ -234,9 +234,18 @@ To create a pipe from which to read the output of @ls@:

(Continue reading)

headers

Evan Laforge | 23 Feb 02:52

Re: documentation patch for process

Any interest in applying this?  I don't think I have permissions.

Or should I get permissions somehow?

On Wed, Feb 8, 2012 at 1:25 PM, Evan Laforge <qdunkan <at> gmail.com> wrote:
> I recently burned some time because I didn't realize that
> System.Process.createProcess doesn't report when the binary isn't
> found.  I guess I was used to that behaviour from python's subprocess
> module, which goes to some effort to report the error from the
> fork()ed child when exec() fails.  After a failed solution, I did some
> poking around in the source to see exactly what haskell's process
> does.
>
> In the interests of saving someone else that time, I submit a patch to
> process to add some documentation.  I'm not sure how to do a 'darcs
> send' with git, but here's the patch:
>
> % git log | head
> commit 5a46937961b3400fa58ccffc785d0de8c1c01d94
> Author: Evan Laforge <qdunkan <at> gmail.com>
> Date:   Wed Feb 8 13:25:16 2012 -0800
>
>    More detailed haddock for createProcess: document what happens if
>    the binary is not found
>
> commit c8b30a6f1d493ab724f2da05dbc49496b119a051
> Author: Simon Marlow <marlowsd <at> gmail.com>
> Date:   Mon Jan 16 16:25:34 2012 +0000
>
> % git diff HEAD\^

(Continue reading)

headers

Evan Laforge | 12 Mar 04:14

Re: documentation patch for process

On Wed, Feb 22, 2012 at 5:52 PM, Evan Laforge <qdunkan <at> gmail.com> wrote:
> Any interest in applying this?  I don't think I have permissions.
>
> Or should I get permissions somehow?

I guess I'll give up on this eventually if there's no interest.  But
it would still be nice to have more documentation.

Going once... going twice...

headers

Simon Marlow | 16 Apr 17:41

Re: documentation patch for process

My apologies, I missed this:

On 08/02/2012 21:25, Evan Laforge wrote:

> % git diff HEAD\^
> diff --git a/System/Process.hs b/System/Process.hs
> index f3a8f9b..a372228 100644
> --- a/System/Process.hs
> +++ b/System/Process.hs
> @@ -234,9 +234,18 @@ To create a pipe from which to read the output of @ls@:
>   To also set the directory in which to run @ls@:
>
>   >    (_, Just hout, _, _)<-
> ->        createProcess (proc "ls" []){ cwd = Just "\home\bob",
> +>        createProcess (proc "ls" []){ cwd = Just "/home/bob",
>   >                                      std_out = CreatePipe }
>
> +Note that this does /not/ throw an error if the binary is not found,
> +or not executable.  Instead, the process will fail with the exit code 127.
> +But you can't rely on it failing quickly, because it may e.g. hang up
> +searching the PATH on a slow NFS mount.  Since there's no way to tell when
> +the exec() has succeeded, the only way to reliably know if the createProcess
> +failed is to 'waitForProcess'.
> +
> +If the CreateProcess record's 'cwd' directory doesn't exist, the exit code
> +will be 126.
>   -}

This isn't true on Windows, so at least the comment should be qualified 
to that effect.

(Continue reading)