Prompt selectors

Prompt selectors are useful when you want to programmatically select a prompt based on the type of model you are using in a chain. This is especially relevant when swapping chat models and LLMs.

The interface for prompt selectors is quite simple:

abstract class BasePromptSelector {
  abstract getPrompt(llm: BaseLanguageModel): BasePromptTemplate;
}

The getPrompt method takes in a language model and returns an appropriate prompt template.

We currently offer a ConditionalPromptSelector that allows you to specify a set of conditions and prompt templates. The first condition that evaluates to true will be used to select the prompt template.

const QA_PROMPT_SELECTOR = new ConditionalPromptSelector(DEFAULT_QA_PROMPT, [
  [isChatModel, CHAT_PROMPT],
]);

This will return DEFAULT_QA_PROMPT if the model is not a chat model, and CHAT_PROMPT if it is.

The example below shows how to use a prompt selector when loading a chain:

const loadQAStuffChain = (
  llm: BaseLanguageModel,
  params: StuffQAChainParams = {}
) => {
  const { prompt = QA_PROMPT_SELECTOR.getPrompt(llm) } = params;
  const llmChain = new LLMChain({ prompt, llm });
  const chain = new StuffDocumentsChain({ llmChain });
  return chain;
};