Just to be clear: a failure when redefining a module is intended behaviour since Livebook 0.8.0 (see the changelog about “Improved reproducibility of module definitions”). That’s what you’re seeing. You previously were running on an older version of Livebook that was ok with redefining modules (with the problem of not being fully reproducible, as José mentioned) which is why you had no problems back then. Nothing in Elixir itself changed in any way, regarding this. Livebook is more restrictive to make sure all livebooks are reproducible (run in the same way, no matter in which order you execute the cells). Regular Elixir allows you to redefine modules (it emits a warning if you do) afaik.
linusdm
josevalim
Creator of Elixir
That’s exactly the issue. Module names are global, so how can you make only subsequent cells see a given module definition? Even if you say: “well, we will purge and swap module versions before execution”, you can still have long-running processes and other functionality that will now be swapping modules on the fly.
Redefining a module is global mutable state and, if you want reproducible notebooks, then it won’t work.
3
linusdm
Ah yes, now I see where my thinking was not correct. I totally forgot about the concurrent aspects of running Elixir code 
.
There would indeed be no way to make such a system behave consistent. Thanks for clarifying!
1
vgrechin
Thank you very, @linusdm for the detailed explanation of Livebook internals, but still can not observe evidence of the regression occurred in 0.8.0. When I tried to build 0.7.2 with Elixir 1.15-rc.2 just encountered a severe run-time error:
00:44:12.714 [error] #PID<0.521.0> running LivebookWeb.Endpoint (connection #PID<0.520.0>, stream id 1) terminated
Server: livebook.sleipner.ru:80 (http)
Request: GET /
** (exit) an exception was raised:
** (FunctionClauseError) no function clause matching in Livebook.Hubs.to_struct/1
(livebook 0.7.2) lib/livebook/hubs.ex:104: Livebook.Hubs.to_struct(%{hub_emoji: "🏠", hub_name: "My Hub", id: "personal-hub", secret_key: "4oB-wLUGbX8SbVcfb6gzG4q4-8wSmmPvXOXmS7y2_wdMiyvSy9IDPr-83n2L7Dh28J2V_uDljhFjVtQ_v46fdw"})
(elixir 1.15.0-rc.2) lib/enum.ex:1693: Enum."-map/2-lists^map/1-1-"/2
(livebook 0.7.2) lib/livebook/hubs.ex:24: Livebook.Hubs.fetch_metadatas/0
(livebook 0.7.2) lib/livebook_web/live/hooks/sidebar_hook.ex:12: LivebookWeb.SidebarHook.on_mount/4
(phoenix_live_view 0.18.2) lib/phoenix_live_view/lifecycle.ex:148: anonymous fn/4 in Phoenix.LiveView.Lifecycle.mount/3
(phoenix_live_view 0.18.2) lib/phoenix_live_view/lifecycle.ex:183: Phoenix.LiveView.Lifecycle.reduce_socket/3
(phoenix_live_view 0.18.2) lib/phoenix_live_view/utils.ex:319: anonymous fn/6 in Phoenix.LiveView.Utils.maybe_call_live_view_mount!/5
(telemetry 1.2.1) /tmp/mix-local-installer-fetcher-U5e5yQ/deps/telemetry/src/telemetry.erl:321: :telemetry.span/3
00:44:17.180 [error] #PID<0.527.0> running LivebookWeb.Endpoint (connection #PID<0.526.0>, stream id 1) terminated
Server: livebook.sleipner.ru:80 (http)
Request: GET /
** (exit) an exception was raised:
** (FunctionClauseError) no function clause matching in Livebook.Hubs.to_struct/1
(livebook 0.7.2) lib/livebook/hubs.ex:104: Livebook.Hubs.to_struct(%{hub_emoji: "🏠", hub_name: "My Hub", id: "personal-hub", secret_key: "4oB-wLUGbX8SbVcfb6gzG4q4-8wSmmPvXOXmS7y2_wdMiyvSy9IDPr-83n2L7Dh28J2V_uDljhFjVtQ_v46fdw"})
(elixir 1.15.0-rc.2) lib/enum.ex:1693: Enum."-map/2-lists^map/1-1-"/2
(livebook 0.7.2) lib/livebook/hubs.ex:24: Livebook.Hubs.fetch_metadatas/0
(livebook 0.7.2) lib/livebook_web/live/hooks/sidebar_hook.ex:12: LivebookWeb.SidebarHook.on_mount/4
(phoenix_live_view 0.18.2) lib/phoenix_live_view/lifecycle.ex:148: anonymous fn/4 in Phoenix.LiveView.Lifecycle.mount/3
(phoenix_live_view 0.18.2) lib/phoenix_live_view/lifecycle.ex:183: Phoenix.LiveView.Lifecycle.reduce_socket/3
(phoenix_live_view 0.18.2) lib/phoenix_live_view/utils.ex:319: anonymous fn/6 in Phoenix.LiveView.Utils.maybe_call_live_view_mount!/5
(telemetry 1.2.1) /tmp/mix-local-installer-fetcher-U5e5yQ/deps/telemetry/src/telemetry.erl:321: :telemetry.span/3
00:44:19.074 [error] #PID<0.533.0> running LivebookWeb.Endpoint (connection #PID<0.532.0>, stream id 1) terminated
Server: livebook.sleipner.ru:80 (http)
Request: GET /
** (exit) an exception was raised:
** (FunctionClauseError) no function clause matching in Livebook.Hubs.to_struct/1
(livebook 0.7.2) lib/livebook/hubs.ex:104: Livebook.Hubs.to_struct(%{hub_emoji: "🏠", hub_name: "My Hub", id: "personal-hub", secret_key: "4oB-wLUGbX8SbVcfb6gzG4q4-8wSmmPvXOXmS7y2_wdMiyvSy9IDPr-83n2L7Dh28J2V_uDljhFjVtQ_v46fdw"})
(elixir 1.15.0-rc.2) lib/enum.ex:1693: Enum."-map/2-lists^map/1-1-"/2
(livebook 0.7.2) lib/livebook/hubs.ex:24: Livebook.Hubs.fetch_metadatas/0
(livebook 0.7.2) lib/livebook_web/live/hooks/sidebar_hook.ex:12: LivebookWeb.SidebarHook.on_mount/4
(phoenix_live_view 0.18.2) lib/phoenix_live_view/lifecycle.ex:148: anonymous fn/4 in Phoenix.LiveView.Lifecycle.mount/3
(phoenix_live_view 0.18.2) lib/phoenix_live_view/lifecycle.ex:183: Phoenix.LiveView.Lifecycle.reduce_socket/3
(phoenix_live_view 0.18.2) lib/phoenix_live_view/utils.ex:319: anonymous fn/6 in Phoenix.LiveView.Utils.maybe_call_live_view_mount!/5
(telemetry 1.2.1) /tmp/mix-local-installer-fetcher-U5e5yQ/deps/telemetry/src/telemetry.erl:321: :telemetry.span/3
0
pasniak
New joiner here. It’s very unintuitive. Wouldn’t a solution be to restart a livebook (a bit like jupyter restarts a kernel wiping all state)?
(I am on mac (v.0.14.5) but could not find a way to restart.)
0