IEx - Expose API to evaluate code inside IEx session for REPL Integrations

rekkice

I’m building an editor integration to evaluate Elixir code in an IEx session. While Code.eval_string/3 allows tracking variable bindings, i think there’s currently no way to persist the environment (aliases, imports, etc.) between evaluations using this approach.

Use Case:

User is using an editor to send code to IEx (through a named pipe, e.g.), which is then read by a custom module defined in .iex.exs.
User defines alias MyApp.Module in one evaluation.
In subsequent evaluations, they expect Module.function() to work (as if it would in a regular IEx shell).

Proposal:
Expose a public API to evaluate code directly in the IEx instance, e.g.:

# it could be a helper function
result = IEx.Helpers.eval_string("IO.puts(123)")

# or maybe work by directly sending a message to IEx’s evaluator process (e.g., using eval_pid() if such a function were available)
send(eval_pid(), {:eval, "IO.puts(123)"})

I think this would make integrating IEx with external tools such as code editors a much easier task. Helix allows piping selected code directly to a Bash command, so i was using that to send code to a named pipe and read that in IEx. IEx is very useful, but i always experience some friction between it and my editor because i have to manually copy and paste code to it.

I found this post from a while ago that suggests something that i think would work for my case, but i tried it on Elixir 1.18.1 with OTP 26 and it didn’t work, maybe because it’s not a public API.

I’d love to hear if others have faced similar challenges or if there’s an existing approach i might have missed. I’d also be happy to contribute to this implementation if there’s interest, though I’m still learning Elixir and don’t have experience with Erlang.

3 comments

#iex #integration #code-editors

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2025-02-10 22:28:39 UTC

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rekkice

I also found this suggestion made recently:

Maybe exposing this API would also help with the ongoing nREPL efforts?

Post #1

v0idpwn

Hi,

I think most of what you want is achievable with Code:

def iterative_eval(code, bindings \\ [], env \\ env_for_eval([])) do
  quoted = Code.string_to_quoted(code)
  Code.eval_quoted_with_env(quoted, bindings, env)
end

Which can be used as:

iex(5)> {result, bindings, env} = Repl.iterative_eval("a = 1"); :ok # Using this `:ok` to avoid printing env
:ok
iex(6)> {result, bindings, env} = Repl.iterative_eval("a + 2", bindings, env); :ok
:ok
iex(7)> result
{:ok, 3}
iex(8)> bindings
[a: 1]

It carries the env, hence it carries aliases, requires, etc. To use the env from iex, you can just use __ENV__:

iex(9)> alias Map, as: M
Map
iex(10)> {result, bindings, env} = Repl.iterative_eval("map = M.new()", [], __ENV__); :ok
:ok
iex(11)> result
{:ok, %{}}
iex(12)> bindings
[map: %{}]
iex(13)>

I don’t know if there’s a way to load these bindings/env back in iex, though.

Post #2