From 9296c481bb2061c53cb270b3c9e19f130ca39338 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fabian=20N=2EC=2E=20van=20=C2=B4t=20Hooft?=
 <fnchooft@gmail.com>
Date: Wed, 19 Jul 2023 14:00:47 -0300
Subject: [PATCH] Add erlang-module support

The code is deemed a module definition if the first line
start with "-module(".

In this case the entire code-block is interpreted as
erlang-module and if there are no errors the module is compiled
and loaded.
---
 lib/livebook/runtime/evaluator.ex | 79 +++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/lib/livebook/runtime/evaluator.ex b/lib/livebook/runtime/evaluator.ex
index 7043eb5b7021..fdc59443f4bf 100644
--- a/lib/livebook/runtime/evaluator.ex
+++ b/lib/livebook/runtime/evaluator.ex
@@ -675,6 +675,85 @@ defmodule Livebook.Runtime.Evaluator do
   end
 
   defp eval(:erlang, code, binding, env) do
+    try do
+      is_module = String.starts_with?(code, "-module(")
+
+      case is_module do
+        true -> eval_module(:erlang, code, binding, env)
+        false -> eval_statements(:erlang, code, binding, env)
+      end
+    catch
+      kind, error ->
+        stacktrace = prune_stacktrace(:erl_eval, __STACKTRACE__)
+        {{:error, kind, error, stacktrace}, []}
+    end
+  end
+
+  # Simple Erlang Module - helper functions
+  # ------------------------------------------------------------------------
+  # In order to handle the expression in their forms - separate per {:dot,_}
+  defp not_dot({:dot, _}) do
+    false
+  end
+
+  defp not_dot(_) do
+    true
+  end
+
+  # A list of scanned token - must be seperated per dot, in order to feed them
+  # into the :erl_parse.parse_form function.
+  defp tokens_to_forms(tokens) do
+    tokens_to_forms(tokens, [])
+  end
+
+  defp tokens_to_forms([], acc) do
+    :lists.reverse(acc)
+  end
+
+  defp tokens_to_forms(tokens, acc) do
+    form = :lists.takewhile(&not_dot/1, tokens)
+    [dot | rest] = :lists.dropwhile(&not_dot/1, tokens)
+    tokens_to_forms(rest, [{form ++ [dot]}] ++ acc)
+  end
+
+  # Create module - tokens from string
+  # Based on: https://stackoverflow.com/questions/2160660/how-to-compile-erlang-code-loaded-into-a-string
+  # The function will first assume that code starting with -module( is a erlang module definition
+
+  # Step 1: Scan the code
+  # Step 2: Convert to forms
+  # Step 3: Extract module name
+  # Step 4: Compile and load
+  defp eval_module(:erlang, code, binding, env) do
+    try do
+      {:ok, tokens, _} = :erl_scan.string(String.to_charlist(code), {1, 1}, [:text])
+
+      form_statements = tokens_to_forms(tokens)
+
+      forms =
+        Enum.map(
+          form_statements,
+          fn {form_statement} ->
+            {:ok, form} = :erl_parse.parse_form(form_statement)
+            form
+          end
+        )
+
+      # First statement - form = module definition
+      {:attribute, _, :module, module_name} = hd(forms)
+
+      # Compile the forms from the code-block
+      {:ok, _, binary_module} = :compile.forms(forms)
+      :code.load_binary(module_name, ~c"nofile", binary_module)
+      {{:ok, ~c"erlang module successfully compiled", binding, env}, []}
+    catch
+      kind, error ->
+        stacktrace = prune_stacktrace(:erl_eval, __STACKTRACE__)
+        {{:error, kind, error, stacktrace}, []}
+    end
+  end
+
+  defp eval_statements(:erlang, code, binding, env) do
     try do
       erl_binding =
         Enum.reduce(binding, %{}, fn {name, value}, erl_binding ->