Create a module in memory, refresh/reload on change

It’s one of those “if you try it, you can figure it out” questions. I’m just hoping someone has already done this before and has some quick tips or a link to look at :slight_smile:

The meat of the question is: I have something in a file (data, or a custom DSL, or anything, really). Using this something, I want to create and compile an Elixir module and load it into the running application. When that something changes (let’s say, a file watcher tells me that contents have changed), I want to re-create/re-compile that module and reload it.

I know that I should start looking at Module.create/3. Perhaps there are other things I can/should look at and consider?

You might use @external_resource attribute on a module…

If the external resource file change, the module will recompile.

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You could try Code.eval_string/3 if you want to parse the changed “something” file from within Elixir to produce a string representation of the module def.

Alternatively Code.eval_file/2 if you dynamically write/update an .ex file from your “something” file.


This is compilation-time dependency, which helps to mark a module as “recompilation needed” for the regular elixir compiler when say mix compile is to be invoked next time. It has zero value here, unfortunately.

Yes, kinda. There is a pitfall one should be aware of: the module recompilation is not instant.

I would spawn the process as gateway access to the module to be recompiled that both recompiles whatever is needed and its mailbox acts as a queue for both subsequent recompilations and all the interactions with this module. That way one can be sure that the module gets accessed if and only it’s available.

Please note, that Module.create/3 accepts an AST. If you want to load a regular .ex[s] file, use Code.eval_file/2 as suggested by @03juan.


Oops, my bad… I did not catch it should be for runtime.

Good point/catch about the queue. Especially if I want this to be based on a custom DSL or custom data, compilation will definitely not be instant.