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37 lines
1.6 KiB
Plaintext
37 lines
1.6 KiB
Plaintext
---
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sidebar_class_name: hidden
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---
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# LangChain Expression Language (LCEL)
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LangChain Expression Language or LCEL is a declarative way to easily compose chains together.
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There are several benefits to writing chains in this manner (as opposed to writing normal code):
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**Async, Batch, and Streaming Support**
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Any chain constructed this way will automatically have full sync, async, batch, and streaming support.
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This makes it easy to prototype a chain in a Jupyter notebook using the sync interface, and then expose it as an async streaming interface.
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**Fallbacks**
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The non-determinism of LLMs makes it important to be able to handle errors gracefully.
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With LCEL you can easily attach fallbacks to any chain.
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**Parallelism**
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Since LLM applications involve (sometimes long) API calls, it often becomes important to run things in parallel.
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With LCEL syntax, any components that can be run in parallel automatically are.
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**Seamless LangSmith Tracing Integration**
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As your chains get more and more complex, it becomes increasingly important to understand what exactly is happening at every step.
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With LCEL, **all** steps are automatically logged to [LangSmith](https://smith.langchain.com) for maximal observability and debuggability.
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#### [Interface](/docs/expression_language/interface)
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The base interface shared by all LCEL objects
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#### [How to](/docs/expression_language/how_to)
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How to use core features of LCEL
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#### [Cookbook](/docs/expression_language/cookbook)
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Examples of common LCEL usage patterns
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#### [Why use LCEL](/docs/expression_language/why)
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A deeper dive into the benefits of LCEL
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