### Quick Start: OpenAI Chat Integration

Source: https://docs.rs/langchainrust

This example demonstrates how to initialize and use the OpenAIChat model for a basic chat interaction. Ensure the OPENAI_API_KEY environment variable is set.

```rust
use langchainrust::{OpenAIChat, OpenAIConfig, BaseChatModel};
use langchainrust::schema::Message;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = OpenAIConfig {
        api_key: std::env::var("OPENAI_API_KEY")?,
        base_url: "https://api.openai.com/v1".to_string(),
        model: "gpt-3.5-turbo".to_string(),
        ..Default::default()
    };
    
    let llm = OpenAIChat::new(config);
    
    let response = llm.chat(vec![
        Message::system("You are a helpful assistant."),
        Message::human("What is Rust?"),
    ], None).await?;
    
    println!("{}", response.content);
    Ok(())
}
```

--------------------------------

### BM25 Keyword Search Example

Source: https://docs.rs/langchainrust

Demonstrates how to use the BM25Retriever for keyword search. Documents are added to the retriever, and then a search is performed to find relevant documents based on a query.

```rust
use langchainrust::{BM25Retriever, Document};

let mut retriever = BM25Retriever::new();

retriever.add_documents_sync(vec![
    Document::new("Rust is a systems programming language"),
    Document::new("Python is a scripting language"),
]);

let results = retriever.search("systems programming", 3);

for result in results {
    println!("Document: {}", result.document.content);
    println!("Score: {}", result.score);
}


```

--------------------------------

### Initialize Chat Models from Environment

Source: https://docs.rs/langchainrust

This snippet shows how to initialize various chat models, including DeepSeek, Moonshot, Anthropic, and Ollama, using environment variables or model names.

```rust
use langchainrust::{
    DeepSeekChat, MoonshotChat,
    AnthropicChat, OllamaChat,
};

let deepseek = DeepSeekChat::from_env();
let moonshot = MoonshotChat::with_model("moonshot-v1-128k");
let claude = AnthropicChat::from_env();
let ollama = OllamaChat::new("llama3.2");


```

--------------------------------

### Run Tests

Source: https://docs.rs/langchainrust

Execute the project's tests using the cargo test command.

```bash
cargo test

```

--------------------------------

### Langchain Rust Architecture Overview

Source: https://docs.rs/langchainrust

This diagram illustrates the layered architecture of the langchainrust library, showing its components for LLM, Embeddings, Agent, Retrieval, and Utility layers.

```text
┌─────────────────────────────────────────────────────────────┐
│                      langchainrust                           │
├─────────────────────────────────────────────────────────────┤
│  LLM Layer                                                   │
│  ├── OpenAIChat / OllamaChat                                 │
│  ├── DeepSeek / Moonshot / Zhipu / Qwen (OpenAI compatible) │
│  ├── AnthropicChat (Claude API)                              │
│  ├── GeminiChat                                              │
│  ├── Function Calling (bind_tools)                          │
│  └── Streaming (stream_chat)                                │
├─────────────────────────────────────────────────────────────┤
│  Embeddings Layer                                            │
│  ├── OpenAIEmbeddings / DeepSeekEmbeddings                   │
│  └── QwenEmbeddings / MockEmbeddings                         │
├─────────────────────────────────────────────────────────────┤
│  Agent Layer                                                 │
│  ├── ReActAgent / FunctionCallingAgent                      │
│  ├── AgentExecutor                                          │
│  └── LangGraph (StateGraph, Subgraph, Parallel)             │
├─────────────────────────────────────────────────────────────┤
│  Retrieval Layer                                             │
│  ├── RAG (TextSplitter, VectorStore)                        │
│  ├── BM25 (Keyword Search, AutoMerging)                     │
│  ├── Hybrid (BM25 + Vector, RRF Fusion)                     │
│  └── HyDE / MultiQuery / Reranking                          │
│  └── Storage (InMemory, Qdrant, MongoDB)                    │
├─────────────────────────────────────────────────────────────┤
│  Utility Layer                                               │
│  ├── Memory (Buffer, Window, Summary)                       │
│  ├── Chains (LLMChain, SequentialChain)                     │
│  ├── Prompts (PromptTemplate, ChatPromptTemplate)           │
│  ├── Tools (Calculator, DateTime, URLFetch)                 │
│  ├── Output Parsers                                         │
│  ├── LLM Cache                                              │
│  └── Callbacks (LangSmith, StdOut, multipart batch)         │
└─────────────────────────────────────────────────────────────┘
```

--------------------------------

### Add Langchain Rust to Cargo.toml

Source: https://docs.rs/langchainrust

Add the langchainrust crate to your project's dependencies in Cargo.toml. Optional features can be enabled for specific integrations like MongoDB, Qdrant, Redis, or SQLite storage.

```toml
[dependencies]

langchainrust = "0.2.18"

tokio = { version = "1.0", features = ["full"] }



# Optional features

langchainrust = { version = "0.2.18", features = ["mongodb-persistence"] }  # MongoDB storage

langchainrust = { version = "0.2.18", features = ["qdrant-integration"] }    # Qdrant vector DB

langchainrust = { version = "0.2.18", features = ["redis-storage"] }         # Redis storage

langchainrust = { version = "0.2.18", features = ["sqlite-storage"] }        # SQLite storage
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.