How Can We Chain PromptTemplate with PromptTemplate

[DragonMengLong]

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Feature request

I am wondering whether we chain the PromptTemplate together just like how we chain the PromptTemplate and LLM using "|" when i need to use one PromptTemplate to wrap the other. It's different with prompt composition or partial prompt templates.

like this "prompt_template | prompt_template | prompt_template | llm"

Motivation

I think it will be more convenient if we can just simply chain two PromptTemplate together specifically when I want to like change all my previous PromptTemplate code, it will be easier to maintain the code. 🙂

Proposal

I find we can't directly chain two PromptTemplate together like " prompt_template | prompt_template" because the previous one return a PromptValue and the after one takes a str, and we can't simply specify in the template when we instantiate the after PromptTemplate like "{input.text}" because if I do that, the input_variables will become "input.text" rather than "input"

So i write a PromptGlue inheriting the Runnable and implement the invoke methord. And Now we can chain two PromptTemplate together like this "fewshot_prompt_template | prompt_glue | prompt_template | llm".

Example Code

class PromptGlue(Runnable):
    def invoke(self, input, config: RunnableConfig | None = None):
        return input.text
gule = PromptGlue()
prompt_template = fewshot_prompt_template | gule | system_prompt_template

[rsk2327]

You can just pass a function through RunnableLambda that converts the PromptValue from first element into string before passing it to the second element.

You can find a very similar example in the note that I published : https://medium.com/p/925aa077227e.

If you check out Example 1, its the same problem statement. Merging the output of one prompt template with another.