Re: GWL 0.5 fails with plain packages

[Olivier Dion via <gwl-devel@gnu.org>]

On Sat, 30 Jul 2022, Liliana Marie Prikler <liliana.prikler@ist.tugraz.at> wrote:

> but it raises more questions.  Like "why is package-ouput a object-
> property?"

I invite you to read this thread
<https://lists.gnu.org/archive/html/gwl-devel/2022-04/msg00009.html> and
the one in the following month for all the details.

But the short answer is that outputs are not needed by GWL except at a
single place (gwl/processes.scm:702).  Changing all the matching
patterns used by GWL to handle new cases was deemed too cumbersome.  I
found that object properties -- or data layering -- was an elegant and
none invasive solution for adding outputs support to GWL.  I just forgot
to add this particular case that you had :-).

Maybe Ricardo has more to say on that.

> and "wouldn't this break if someone needed two different
> outputs of the same package in a process or even anywhere in the
> workflow?"

I don't think so.  I have a workflow that requires `out' and `debug'
outputs to instrument packages.  Works flawlessly.

Example:
--8<---------------cut here---------------start------------->8---
use-modules : gnu packages base
use-modules : gnu packages gcc

process greet
  packages
    list
      list hello "out"
      list gcc "out"
      list gcc "lib"
      list gcc "debug"
  # { hello }

workflow simple-wisp
  processes
    list greet
--8<---------------cut here---------------end--------------->8---

-- 
Olivier Dion
oldiob.dev