Deprecate usage of parse_transforms

[josevalim]

Elixir supports Erlang parse transforms but if we want to eventually perform less compiler steps and even compile directly to core one day, we will no longer be able to support those.

[michalmuskala]

If this is going to happen, we need good alternatives. The only two places, I've used parse transforms were to make :dbg.fun2ms/1 or :ets.fun2ms/1 work. If there are convenient alternatives for those two use cases, I see no downsides in going forward with this change.

[fishcakez]

Note we don't currently support those two, only a small subset of features work for those functions. To use them you already need to use another library or an Erlang module.

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On 12 Feb 2017 6:59 pm, "Michał Muskała" ***@***.***> wrote: If this is going to happen, we need good alternatives. The only two places, I've used parse transforms were to make :dbg.fun2ms/1 or :ets.fun2ms/1 work. If there are convenient alternatives, I see no downsides in going forward with this change. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#5762 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AB6JTdo3YKqXvnmLYvtufFm67jTTOzP9ks5rb1adgaJpZM4L-jxp> .

[josevalim]

@michalmuskala this may be a good starting point: https://github.com/ericmj/ex2ms

[holsee]

What do you folks think this will mean for elixir projects which use things like Erlang's lager library which leverages parse transforms to remove logging levels that are not desired for a given build type?

I am working on erlang-lager/lager#348 "Add docs about using lager in elixir" and that is how I stubbled upon this issue. I don't want to be recommending an approach that would not be supported in the near future.

[josevalim]

This is one of the few cases where I would recommend wrapping an Erlang library in an elixir library and provide the same API with macros. Parse_transforms work on Erlang AST and being dependent on the Erlang AST is going to limit the improvements we can do to the Elixir compiler. -- *José Valimwww.plataformatec.com.br <http://www.plataformatec.com.br/>Founder and Director of R&D*