From 63916cfe3556788bc015ab9b9456e7087823ff2d Mon Sep 17 00:00:00 2001
From: Harrison Chase <hw.chase.17@gmail.com>
Date: Tue, 26 Dec 2023 12:19:50 -0800
Subject: [PATCH] [core] langauge model like (#15180)

---
 libs/core/langchain_core/language_models/__init__.py      | 2 ++
 libs/core/langchain_core/language_models/base.py          | 8 +++++---
 .../core/tests/unit_tests/language_models/test_imports.py | 1 +
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/libs/core/langchain_core/language_models/__init__.py b/libs/core/langchain_core/language_models/__init__.py
index 4c2e597dddf..b86de1cdb13 100644
--- a/libs/core/langchain_core/language_models/__init__.py
+++ b/libs/core/langchain_core/language_models/__init__.py
@@ -1,6 +1,7 @@
 from langchain_core.language_models.base import (
     BaseLanguageModel,
     LanguageModelInput,
+    LanguageModelLike,
     LanguageModelOutput,
     get_tokenizer,
 )
@@ -16,4 +17,5 @@ __all__ = [
     "LanguageModelInput",
     "get_tokenizer",
     "LanguageModelOutput",
+    "LanguageModelLike",
 ]
diff --git a/libs/core/langchain_core/language_models/base.py b/libs/core/langchain_core/language_models/base.py
index f48f83b37f4..b590e0df84f 100644
--- a/libs/core/langchain_core/language_models/base.py
+++ b/libs/core/langchain_core/language_models/base.py
@@ -17,7 +17,7 @@ from typing_extensions import TypeAlias
 
 from langchain_core.messages import AnyMessage, BaseMessage, get_buffer_string
 from langchain_core.prompt_values import PromptValue
-from langchain_core.runnables import RunnableSerializable
+from langchain_core.runnables import Runnable, RunnableSerializable
 from langchain_core.utils import get_pydantic_field_names
 
 if TYPE_CHECKING:
@@ -49,11 +49,13 @@ def _get_token_ids_default_method(text: str) -> List[int]:
 
 
 LanguageModelInput = Union[PromptValue, str, List[BaseMessage]]
-LanguageModelOutput = TypeVar("LanguageModelOutput")
+LanguageModelOutput = Union[BaseMessage, str]
+LanguageModelLike = Runnable[LanguageModelInput, LanguageModelOutput]
+LanguageModelOutputVar = TypeVar("LanguageModelOutputVar", BaseMessage, str)
 
 
 class BaseLanguageModel(
-    RunnableSerializable[LanguageModelInput, LanguageModelOutput], ABC
+    RunnableSerializable[LanguageModelInput, LanguageModelOutputVar], ABC
 ):
     """Abstract base class for interfacing with language models.
 
diff --git a/libs/core/tests/unit_tests/language_models/test_imports.py b/libs/core/tests/unit_tests/language_models/test_imports.py
index 348111f8511..65d627c56fd 100644
--- a/libs/core/tests/unit_tests/language_models/test_imports.py
+++ b/libs/core/tests/unit_tests/language_models/test_imports.py
@@ -9,6 +9,7 @@ EXPECTED_ALL = [
     "LanguageModelInput",
     "LanguageModelOutput",
     "get_tokenizer",
+    "LanguageModelLike",
 ]