diff --git a/swh/lister/elm/__init__.py b/swh/lister/elm/__init__.py
new file mode 100644
index 0000000000000000000000000000000000000000..614d8efda1e5554fa17937f75b1ece99548a234a
--- /dev/null
+++ b/swh/lister/elm/__init__.py
@@ -0,0 +1,76 @@
+# Copyright (C) 2023 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+
+"""
+Elm lister
+==========
+
+`Elm`_ is a functional language that compiles to JavaScript.
+
+Additional packages for the language can be searched from the `Packages`_ website
+and installed with `elm install`_ command. The Elm packages website also provides a
+`Http Api endpoint`_ listing all available packages.
+
+Elm origins are Git repositories hosted on Github. Each repository must provide its
+packaged releases using the Github release system.
+
+As of July 2023 `Packages`_ list 1746 packages.
+
+Origins retrieving strategy
+---------------------------
+
+To build a list of origins we make a GET request to the `Http Api endpoint`_ that returns
+a Json array of objects.
+The origin url for each package is constructed with the information of corresponding
+`name` entry which represents the suffix of Github repositories (org/project_name).
+
+Page listing
+------------
+
+There is only one page listing all origins url.
+
+Origins from page
+-----------------
+
+The lister is stateless and yields all origins url from one page. It is a list of package
+repository url.
+
+Running tests
+-------------
+
+Activate the virtualenv and run from within swh-lister directory::
+
+ pytest -s -vv --log-cli-level=DEBUG swh/lister/elm/tests
+
+Testing with Docker
+-------------------
+
+Change directory to swh/docker then launch the docker environment::
+
+ docker compose up -d
+
+Then schedule a elm listing task::
+
+ docker compose exec swh-scheduler swh scheduler task add -p oneshot list-elm
+
+You can follow lister execution by displaying logs of swh-lister service::
+
+ docker compose logs -f swh-lister
+
+.. _Elm: https://elm-lang.org/
+.. _Packages: https://package.elm-lang.org/
+.. _elm install: https://guide.elm-lang.org/install/elm.html#elm-install
+.. _Http Api endpoint: https://package.elm-lang.org/search.json
+"""
+
+
+def register():
+ from .lister import ElmLister
+
+ return {
+ "lister": ElmLister,
+ "task_modules": ["%s.tasks" % __name__],
+ }
diff --git a/swh/lister/elm/lister.py b/swh/lister/elm/lister.py
new file mode 100644
index 0000000000000000000000000000000000000000..83a1b84e3d9d6b292294fe98f1e2159072104127
--- /dev/null
+++ b/swh/lister/elm/lister.py
@@ -0,0 +1,74 @@
+# Copyright (C) 2023 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import logging
+from typing import Any, Dict, Iterator, List, Optional
+
+from swh.scheduler.interface import SchedulerInterface
+from swh.scheduler.model import ListedOrigin
+
+from ..pattern import CredentialsType, StatelessLister
+
+logger = logging.getLogger(__name__)
+
+# Aliasing the page results returned by `get_pages` method from the lister.
+ElmListerPage = List[Dict[str, Any]]
+
+
+class ElmLister(StatelessLister[ElmListerPage]):
+ """List Elm packages origins"""
+
+ LISTER_NAME = "elm"
+ VISIT_TYPE = "git" # Elm origins url are Git repositories
+ INSTANCE = "elm"
+
+ SEARCH_URL = "https://package.elm-lang.org/search.json"
+
+ REPO_URL_PATTERN = "https://github.com/{name}"
+
+ def __init__(
+ self,
+ scheduler: SchedulerInterface,
+ credentials: Optional[CredentialsType] = None,
+ max_origins_per_page: Optional[int] = None,
+ max_pages: Optional[int] = None,
+ enable_origins: bool = True,
+ ):
+ super().__init__(
+ scheduler=scheduler,
+ credentials=credentials,
+ instance=self.INSTANCE,
+ url=self.SEARCH_URL,
+ max_origins_per_page=max_origins_per_page,
+ max_pages=max_pages,
+ enable_origins=enable_origins,
+ )
+ self.session.headers.update({"Accept": "application/json"})
+
+ def get_pages(self) -> Iterator[ElmListerPage]:
+ """Yield an iterator which returns 'page'
+
+ It uses the unique Http api endpoint `https://package.elm-lang.org/search.json`
+ to get a list of names corresponding to Github repository url suffixes.
+
+ There is only one page that list all origins urls.
+ """
+ response = self.http_request(self.url)
+ yield response.json()
+
+ def get_origins_from_page(self, page: ElmListerPage) -> Iterator[ListedOrigin]:
+ """Iterate on all pages and yield ListedOrigin instances"""
+ assert self.lister_obj.id is not None
+
+ for entry in page:
+ name: str = entry["name"]
+ repo_url: str = self.REPO_URL_PATTERN.format(name=name)
+
+ yield ListedOrigin(
+ lister_id=self.lister_obj.id,
+ visit_type=self.VISIT_TYPE,
+ url=repo_url,
+ last_update=None,
+ )
diff --git a/swh/lister/elm/tasks.py b/swh/lister/elm/tasks.py
new file mode 100644
index 0000000000000000000000000000000000000000..de9ff97549a2d4472267ccaf0cab1e09d32b78bc
--- /dev/null
+++ b/swh/lister/elm/tasks.py
@@ -0,0 +1,19 @@
+# Copyright (C) 2023 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from celery import shared_task
+
+from swh.lister.elm.lister import ElmLister
+
+
+@shared_task(name=__name__ + ".ElmListerTask")
+def list_elm(**lister_args):
+ """Lister task for Elm lang packages"""
+ return ElmLister.from_configfile(**lister_args).run().dict()
+
+
+@shared_task(name=__name__ + ".ping")
+def _ping():
+ return "OK"
diff --git a/swh/lister/elm/tests/__init__.py b/swh/lister/elm/tests/__init__.py
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
diff --git a/swh/lister/elm/tests/data/https_package.elm-lang.org/search.json b/swh/lister/elm/tests/data/https_package.elm-lang.org/search.json
new file mode 100644
index 0000000000000000000000000000000000000000..cdb20cecc06452dcc75bcbe816abf9da6033c3a5
--- /dev/null
+++ b/swh/lister/elm/tests/data/https_package.elm-lang.org/search.json
@@ -0,0 +1,20 @@
+[
+ {
+ "name": "elm/bytes",
+ "summary": "Work with sequences of bytes (a.k.a. ArrayBuffer, typed arrays, DataView)",
+ "license": "BSD-3-Clause",
+ "version": "1.0.8"
+ },
+ {
+ "name": "STTR13/ziplist",
+ "summary": "List with a selected element that makes impossible state impossible.",
+ "license": "BSD-3-Clause",
+ "version": "1.4.2"
+ },
+ {
+ "name": "cuducos/elm-format-number",
+ "summary": "Format numbers as pretty strings",
+ "license": "BSD-3-Clause",
+ "version": "9.0.1"
+ }
+]
diff --git a/swh/lister/elm/tests/test_lister.py b/swh/lister/elm/tests/test_lister.py
new file mode 100644
index 0000000000000000000000000000000000000000..88511bbbae33a17ce855396d975dc202929044c1
--- /dev/null
+++ b/swh/lister/elm/tests/test_lister.py
@@ -0,0 +1,32 @@
+# Copyright (C) 2023 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.lister.elm.lister import ElmLister
+
+expected_origins = [
+ "https://github.com/STTR13/ziplist",
+ "https://github.com/elm/bytes",
+ "https://github.com/cuducos/elm-format-number",
+]
+
+
+def test_elm_lister(datadir, requests_mock_datadir, swh_scheduler):
+ lister = ElmLister(scheduler=swh_scheduler)
+ res = lister.run()
+
+ assert res.pages == 1
+ assert res.origins == 1 + 1 + 1
+
+ scheduler_origins = swh_scheduler.get_listed_origins(lister.lister_obj.id).results
+
+ assert len(scheduler_origins) == len(expected_origins)
+ assert {
+ (
+ scheduled.visit_type,
+ scheduled.url,
+ scheduled.last_update,
+ )
+ for scheduled in scheduler_origins
+ } == {("git", expected, None) for expected in expected_origins}
diff --git a/swh/lister/elm/tests/test_tasks.py b/swh/lister/elm/tests/test_tasks.py
new file mode 100644
index 0000000000000000000000000000000000000000..cbea3220f94b5c17ee28f7f5d6daec889b4cc4d8
--- /dev/null
+++ b/swh/lister/elm/tests/test_tasks.py
@@ -0,0 +1,31 @@
+# Copyright (C) 2023 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.lister.pattern import ListerStats
+
+
+def test_elm_ping(swh_scheduler_celery_app, swh_scheduler_celery_worker):
+ res = swh_scheduler_celery_app.send_task("swh.lister.elm.tasks.ping")
+ assert res
+ res.wait()
+ assert res.successful()
+ assert res.result == "OK"
+
+
+def test_elm_lister(swh_scheduler_celery_app, swh_scheduler_celery_worker, mocker):
+ # setup the mocked ElmLister
+ lister = mocker.patch("swh.lister.elm.tasks.ElmLister")
+ lister.from_configfile.return_value = lister
+ stats = ListerStats(pages=42, origins=42)
+ lister.run.return_value = stats
+
+ res = swh_scheduler_celery_app.send_task("swh.lister.elm.tasks.ElmListerTask")
+ assert res
+ res.wait()
+ assert res.successful()
+ assert res.result == stats.dict()
+
+ lister.from_configfile.assert_called_once_with()
+ lister.run.assert_called_once_with()