Checked other resources

• This is a bug, not a usage question.
• I added a clear and descriptive title that summarizes this issue.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
• This is not related to the langchain-community package.
• I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS.

Package (Required)

• langchain
• langchain-openai
• langchain-anthropic
• langchain-classic
• langchain-core
• langchain-model-profiles
• langchain-tests
• langchain-text-splitters
• langchain-chroma
• langchain-deepseek
• langchain-exa
• langchain-fireworks
• langchain-groq
• langchain-huggingface
• langchain-mistralai
• langchain-nomic
• langchain-ollama
• langchain-openrouter
• langchain-perplexity
• langchain-qdrant
• langchain-xai
• Other / not sure / general

Related Issues / PRs

N/A

Reproduction Steps / Example Code (Python)

# ---- Bug 1: Language.PERL not implemented ----
from langchain_text_splitters import RecursiveCharacterTextSplitter, Language

try:
    # PERL exists in enum but is not implemented in separator logic
    RecursiveCharacterTextSplitter.from_language(
        Language.PERL,
        chunk_size=10,
        chunk_overlap=0
    )
except ValueError as e:
    print(f"Bug 1 Error: {e}")


# ---- Bug 2: InMemoryCache eviction bug ----
from langchain_core.caches import InMemoryCache

cache = InMemoryCache(maxsize=2)

cache.update("prompt_1", "llm_1", "val1")
cache.update("prompt_2", "llm_2", "val2")

# Cache is now at maxsize.
# Updating an existing key SHOULD NOT evict another entry.
cache.update("prompt_2", "llm_2", "val2_new_value")

# Expected: prompt_1 still exists
print("Cache keys:", list(cache._cache.keys()))
print("Bug 2: Is prompt_1 still in cache?",
      ("prompt_1", "llm_1") in cache._cache)

Error Message and Stack Trace (if applicable)

# Bug 1
ValueError: Language Language.PERL is not implemented yet!

# Bug 2 (Observed Behavior)
Bug 2: Is prompt_1 still in cache? False

Description

There are two distinct bugs grouped here:

1. Language.PERL is correctly defined in the Language enum, but the switch statement inside get_separators_for_language does not handle it, resulting in a fall-through ValueError instead of appropriately fetching Perl-specific separators.
2. InMemoryCache.update() shrinks the cache incorrectly. When the cache is at its exact maxsize, and you call update() using a key that already exists in the cache, the code checks len(cache) == maxsize and forcefully evicts the oldest entry anyway, lowering the cache size instead of performing an in-place update.

I have already pushed a Branch fixing both issues (adding Perl separators for sub, package, do, eval, etc., and adding an eviction safety guard for InMemoryCache) to my fork and am ready to raise the associated PR closing this issue!

System Info

python3 -m langchain_core.sys_info /opt/homebrew/lib/python3.14/site-packages/langchain_core/_api/deprecation.py:25: UserWarning: Core Pydantic V1 functionality isn't compatible with Python 3.14 or greater. from pydantic.v1.fields import FieldInfo as FieldInfoV1

System Information

OS: Darwin OS Version: Darwin Kernel Version 24.6.0: Wed Nov 5 21:33:59 PST 2025; root:xnu-11417.140.69.705.2~1/RELEASE_ARM64_T8112 Python Version: 3.14.3 (main, Feb 3 2026, 15:32:20) [Clang 17.0.0 (clang-1700.6.3.2)]

Package Information

langchain_core: 1.2.11 langchain: 1.0.7 langchain_community: 0.3.31 langsmith: 0.7.22 langchain_openai: 1.0.3 langgraph_sdk: 0.3.12

Optional packages not installed

langserve

Other Dependencies

aiohttp: 3.13.4 dataclasses-json: 0.6.7 httpx: 0.28.1 httpx-sse: 0.4.3 jsonpatch: 1.33 langgraph: 1.0.8 numpy: 2.4.4 openai: 2.30.0 orjson: 3.11.7 packaging: 26.0 pydantic: 2.12.5 pydantic-settings: 2.13.1 pytest: 9.0.2 PyYAML: 6.0.3 pyyaml: 6.0.3 requests: 2.33.0 requests-toolbelt: 1.0.0 rich: 15.0.0 SQLAlchemy: 2.0.48 tenacity: 9.1.4 tiktoken: 0.12.0 typing-extensions: 4.15.0 uuid-utils: 0.14.1 xxhash: 3.6.0 zstandard: 0.25.0