defmodule in livebook sometimes raises compilation errors (Module is already defined)

[linusdm]

Can someone shed light on how LB integrates with defmodule?

I sometimes observe that modules cannot be redefined, resulting in a compilation error (** (CompileError) #cell:xyz:1: module MyModule is already defined). Re-running the same code cell that defines a module, does not seem to have this problem, which is what I don't understand. I'd expect the same error there. If you try to redefine a module with the same name in another cell, the compilation error is raised.

This is a bit unfortunate, for example when I try to import this LB: https://github.com/BrooklinJazz/elixir_newbie_website_v1/blob/master/livebook/writing-tests-in-livebook.livemd. The subsequent definitions with the same module name fail.

Did this behaviour change somehow in recent versions of LB? Because I'd expect that the the author of the referenced notebook (@BrooklinJazz) would've had the same issues when redefining modules.

Or is it just not a good idea to do such things (using the same module name in different code cells)? I realise that the defmodule construct triggers compilation (which probably is not the case for the regular code in the cells), which might change things a bit.

Thanks in advance!

[jonatanklosko]

Hey @linusdm! This is expected, we now track modules and the given module can only be defined in a single cell to improve reproducibility (since the module is overridden globally). Also see DockYard-Academy/curriculum#622.

[linusdm]

Ok, great! that clears things up for me.