Behaviour for query expansion in the Agent pipeline.

The expander adds synonyms, related terms, and alternative phrasings to improve document retrieval coverage.

Built-in Implementations

• Arcana.Agent.Expander.LLM - Uses your LLM to expand queries (default)

Implementing a Custom Expander

defmodule MyApp.ThesaurusExpander do
  @behaviour Arcana.Agent.Expander

  @impl true
  def expand(question, _opts) do
    expanded = question <> " " <> lookup_synonyms(question)
    {:ok, expanded}
  end

  defp lookup_synonyms(question) do
    # Your synonym lookup logic
    ""
  end
end

Using a Custom Expander

Agent.new(question, repo: repo, llm: llm)
|> Agent.expand(expander: MyApp.ThesaurusExpander)
|> Agent.search()

Using an Inline Function

Agent.expand(ctx,
  expander: fn question, _opts ->
    {:ok, question <> " programming software development"}
  end
)