Hi,
On 9/13/22 20:27, jgart wrote:
From: jgart <jg...@dismail.de>
To: Guix Help <help-guix@gnu.org>
Cc: Philip McGrath <phi...@philipmcgrath.com>
Bcc:
Subject: Using elm with Guix
Reply-To:
In-Reply-To:
Hi,
I'v been trying to use elm with Guix at the repl and by compiling a
src/Main.elm file and elm doesn't find any of the Guix-installed dependencies:
I think there are a few different things going on here.
```
guix-shell elm make src/Main.elm
Detected problems in 1 module.
-- MODULE NOT FOUND ----------------------------------------------- src/Main.elm
You are trying to import a `Http` module:
10| import Http
^^^^
I checked the "dependencies" and "source-directories" listed in your elm.json,
but I cannot find it! Maybe it is a typo for one of these names?
Set
Dict
Main
Task
Hint: Maybe you want the `Http` module defined in the elm/http package? Running
elm install elm/http should make it available!
```
>
> Is there a way that I'm supposed to be using elm with Guix in order to
> discover the dependencies.
This part of the problem doesn't seem to involve Guix.
As you may know, Elm "module"s (files like "Main.elm" or "Http.elm") are
organized in "project"s, where a project is either a "package" or an
"application". Every Elm "project" must include a file called "elm.json"
declaring the project's structure and dependencies. Unlike many
languages, Elm doesn't have a concept of modules outside of a project,
nor of globally installed packages: when compiling `import Http` in your
"src/Main.elm", Elm will look for an `Http` module that is either part
of the same project---i.e. a file "src/Http.elm", unless anything is
configured unusually---or in one of the Elm packages listed in the
"elm.json" file.
In other words, Elm never "discovers" dependencies. That's true even for
the modules from "elm/core" package!
What this error message is saying is that your "elm.json" file doesn't
declare a dependency on the "elm/http" package, so there's no `Http`
module available. You could edit the "elm.json" file by hand, but you'd
have to get indirect dependencies and versions right. The command
suggested in the error message:
elm install elm/http
will edit your "elm.json" file for you to declare the additional
dependency. For a useful example, look at:
guix build --source elm-todomvc
The usage of this for elm developers using Guix looks undocumented.
What I tried:
```
guix shell elm elm-json elm-html emacs-http
mkdir elm_play
cd elm_play
elm init
elm make src/Main.elm
```
Here, though, we get to some issues that do involve Guix: in particular,
using `guix shell` to install `elm-json` and `elm-html` isn't
(currently?) helpful for interactive development in the way you would
hope. First I'll try to explain two ways of using Guix for Elm
development that do work; then I'll explain the unresolved issues here.
One option is to use Guix to install `elm`, but then let Elm manage
other Elm packages you need for interactive development. This is
analogous to using Guix to install Python or Node, then installing
packages with `pip` or `npm`. (Maybe it's a little better than that, in
that Elm has very stringent requirements enforced by the compiler to
avoid some of the hairy problems with e.g. npm packages.)
Another option is to define a Guix package for your Elm project using
`local-file` in the origin, and then, instead of `elm make`, build your
project with e.g.:
guix build -f elm_play.scm
In that case, `guix import elm` may be useful for any of your packages
that aren't already in Guix, and the package definition for elm-todomvc
would be a good example to imitate. In particular, either you need to
make sure that your "elm.json" file matches the versions of your
dependencies packaged in Guix or you should make use of the the
`patch-application-dependencies` procedure as suggested in the
documentation for `elm-build-system`.
The problem with:
guix shell elm elm-json elm-html elm-http
(I assume you didn't mean `emacs-http`) is that it won't put the built
Elm packages in a place where Elm can find them.
Elm looks for installed packages in a single directory, either "~/.elm"
(IIRC) or the value of the ELM_HOME environment variable, if it's set.
We of course have functions to assemble such a directory in
"guix/build/elm-build-system.scm", and we could expose them either via a
package-generating function (analogous to texlive-updmap.cfg`) or even a
profile hook.
The deeper issue is that Elm sometimes tries to write to existing
"artifacts.dat" files in ELM_HOME: this is also the cause of the caveat
about multiple versions of the same Elm package not tending to coexist
well in a single Guix build environment, even though that's supported at
the Elm level. I haven't dug deep enough into the internals of the Elm
compiler to figure out exactly what's going on.
It's possible that the very limited support for working offline I
patched into Elm for Guix might be enough to work around this, if you
want to set up an environment with an ELM_HOME managed exclusively by
Guix. Alternatively, it could be interesting to explore patching Elm
further to not try to overwrite "artifacts.dat" files and look for
packages in an additive way, perhaps using XDG_DATA_DIRS. If you're
interested in exploring any of that, I wrote comments in
"guix/build/elm-build-system.scm" and
"gnu/packages/patches/elm-offline-package-registry.patch" with ideas,
and IIRC there was some informative discussion upstream at
<https://discourse.elm-lang.org/t/private-package-tool-spec/6779/25> and
maybe related to `elm-test-rs`
<https://github.com/mpizenberg/elm-test-rs>, and probably other places.
If we came up with a nice approach, I hope upstream might be open to
patches, especially since the Elm community is enthusiastic about
immutability.
Anyway, I hope this helps, and let me know how it goes! I'm glad the
support for Elm in Guix so far is interesting, and I think having more
people try it will be the best way to figure out how we might be able to
improve on it.
-Philip
