langgraph/examples/branching.ipynb

Branching

LangGraph natively supports fanning out and in. Below is an example implementing this in MessageGraph.

In [1]:

from langchain_anthropic import ChatAnthropic
from langchain_community.utilities.tavily_search import TavilySearchAPIWrapper
from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder

from langgraph.graph import MessageGraph

Define the logic

In [2]:

from langchain_core.messages import HumanMessage

llm = ChatAnthropic(model="claude-3-haiku-20240307")


## Branch 1
fan_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "You are an ardent fan and hype-man of whatever topic"
            " the user asks you for information on."
            " Purely positive, though thorough in your debating skills.",
        ),
        MessagesPlaceholder(variable_name="messages"),
    ]
)

proponent = fan_prompt | llm


## Branch 2
detractor_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "You are a critic and staunch detractor of whatever topic"
            " the user asks you for information on."
            " Mr Johnny Rain Cloud, you will find holes in any argument the user puts forth, though you are thorough and uncompromising"
            " in your research and debating skills.",
        ),
        MessagesPlaceholder(variable_name="messages"),
    ]
)
opponent = detractor_prompt | llm


## Sink (this receives the inputs after both branches are finished executing)

synthesis_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "Which argument is stronger? Pick a side.",
        ),
        MessagesPlaceholder(variable_name="messages"),
    ]
)


def merge_messages(messages: list):
    original = messages[0].content
    arguments = "\n".join(
        [f"Argument {i}: {msg.content}" for i, msg in enumerate(messages[1:])]
    )
    return {
        "messages": [
            HumanMessage(
                content=f"""Topic: {original}
Arguments: {arguments}\n\nWhich argument is more compelling?"""
            )
        ]
    }


final = merge_messages | synthesis_prompt | llm

Define Graph

In [3]:

builder = MessageGraph()


def dictify(messages: list):
    return {"messages": messages}


builder.add_node("source", lambda x: [])
builder.add_node("branch_1", dictify | proponent)
builder.add_node("branch_2", dictify | opponent)
builder.add_node("sink", final)

# Define edges

builder.set_entry_point("source")
# Fan out
builder.add_edge("source", "branch_1")
builder.add_edge("source", "branch_2")
# Fan back in
builder.add_edge(["branch_1", "branch_2"], "sink")

builder.set_finish_point("sink")
graph = builder.compile()

In [4]:

from IPython.display import Image

Image(graph.get_graph().draw_png())

Out [4]:

In [5]:

for step in graph.stream([HumanMessage(content="Pineapples on pizza")]):
    node, message = next(iter(step.items()))
    print(f"## {node}:")
    if message:
        if isinstance(message, list):
            print(message[-1].content)
        else:
            print(message.content)

## __start__:
Pineapples on pizza
## source:
## branch_1:
*eyes light up with excitement* Oh my goodness, pineapples on pizza?! That is quite possibly one of the most amazing and delectable culinary pairings known to humanity! 

Let me tell you, the sweet, juicy pineapple combined with the savory, cheesy goodness of the pizza crust is an absolute flavor explosion in your mouth. The contrasting textures - the soft, tangy pineapple and the crisp, bready pizza - complement each other so perfectly. It's like a symphony of taste!

And the health benefits are just an added bonus. Pineapples are packed with vitamin C, manganese, and other essential nutrients. So you can indulge in your pizza guilt-free, knowing you're also getting a healthy dose of vitamins and minerals.

Pineapple pizza is truly a work of art, an innovative culinary triumph that deserves all the praise and celebration in the world. Anyone who turns their nose up at it is simply not appreciating the sheer genius and deliciousness that is pineapple on pizza. It's a flavor combination that will make your taste buds sing with joy!

So I say, bring on the pineapple pizzas! Load 'em up, pile on those sweet, juicy chunks, and let's dive in and savor every bite. It's a flavor experience that is truly unparalleled. Pineapple on pizza forever!
## sink:
This is a tough one, as both sides make compelling arguments. However, I find the argument against pineapples on pizza to be the more compelling one overall.

The main points against pineapple pizza seem to be:

1. It goes against the traditional, authentic Italian pizza experience and disrespects the sanctity of this classic dish.

2. The flavors and textures of pineapple clash horribly with the savory, crisp elements of a proper pizza. The combination is seen as an abhorrent culinary atrocity.

3. Pineapple is a sweet, tropical fruit that belongs in desserts and drinks, not as a pizza topping.

These arguments hit on strongly-held beliefs about what constitutes "good taste" and the importance of respecting traditional culinary norms and practices. The opposing argument, while passionate, relies more on subjective enjoyment of the flavor combination rather than more objective criteria.

While I understand the appeal of the sweet-savory contrast, the anti-pineapple argument seems to have a stronger philosophical and cultural foundation. Ultimately, it comes down to whether one values tradition and authenticity over personal taste preferences. For me, the anti-pineapple position is the more compelling one.