[m-users.] Bug in posix.readdir (fixed)

[Julien Fischer]

Hi Volker,

On Fri, 11 Oct 2019, Volker Wysk wrote:

> The readdir/4 predicate from the posix library is buggy. It returns an
> "unknown error code" error for the end of the directory stream.
>
>
> I've fixed it. I've changed the type from
>
> :- pred readdir(dir::in,
> 	        posix.result(string)::out,
> 		io::di, io::uo) is det.
>
> to
>
> :- pred readdir(dir::in,
>                posix.result(maybe(string))::out,
>                io::di, io::uo) is det.
>
>
> The new version returns "posix.ok(yes(File))" for a directory entry,
> and "posix.ok(no)" for the end of the stream.

I don't like returning a maybe type like that, it means you need
two levels of switching at call sites for readdir/4.  I suggest
adding the type:

    :- type readdir_result
         --->	ok(string)
         ;       eof
         ;       error(posix.error).


and using that.

> See the attached file. It should replace the posix.readdir.m file from
> the posix library (after renaming from readdir to posix.readdir).

Thanks for that.  I'll apply that change (except with new return type
above).

Julien.