feat: add tool decorator by akihikokuroda · Pull Request #387 · generative-computing/mellea

akihikokuroda · 2026-01-30T15:09:52Z

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Link to Issue: fix: feat: add decorators for mellea tools #382

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Tests added to the respective file if code was changed
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Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

mergify · 2026-01-30T15:10:26Z

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github-actions · 2026-01-30T15:10:53Z

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jakelorocco · 2026-02-02T14:17:06Z

docs/examples/tools/interpreter_example.py

+# Example: Define a custom tool using the @tool decorator
+@tool
+def get_weather(location: str, days: int = 1) -> dict:
+    """Get weather forecast for a location.
+
+    Args:
+        location: City name
+        days: Number of days to forecast (default: 1)
+    """
+    # Mock implementation
+    return {"location": location, "days": days, "forecast": "sunny", "temperature": 72}
+
+
+@tool(name="custom_calculator")
+def calculate(expression: str) -> float:
+    """Evaluate a mathematical expression.
+
+    Args:
+        expression: Mathematical expression to evaluate
+    """
+    # Simple mock - in production, use safe evaluation
+    return eval(expression)
+
+


Please remove these tool definitions. I don't think they are used in this file.

jakelorocco · 2026-02-02T14:18:01Z

docs/examples/tools/tool_decorator_example.py

+    # Before the decorator, you had to do:
+    # tools = [MelleaTool.from_callable(get_weather), MelleaTool.from_callable(search_web)]


Maybe change this comment to Without the decorator, you can add tools using:

jakelorocco · 2026-02-02T14:27:02Z

mellea/backends/tools.py

+def tool(func: Callable | None = None, *, name: str | None = None) -> Any:
+    """Decorator to mark a function as a Mellea tool.
+
+    This decorator wraps a function to make it usable as a tool without
+    requiring explicit MelleaTool.from_callable() calls. The decorated
+    function can be used both as a normal callable and as a MelleaTool.


I'm not certain about this implementation. I see two main issues:

It diverges from our existing tool implementation. For existing tools, you use .run() to call the underlying function with the appropriate arguments. We should unify this wrapper with that approach. It might require using generics with ParamSpec to get the typing correct for run().

The returned object isn't typed as a Tool by IDEs. I think this confusing because there is no real way to know if what you are passing in is a tool or a regular callable function.

jakelorocco · 2026-02-02T14:28:07Z

mellea/backends/tools.py

+            # Extract MelleaTool from decorated functions
+            if hasattr(tool_instance, "_mellea_tool"):
+                tool_instance = tool_instance._mellea_tool


Shouldn't we be able to pass in the decorated function directly since it's typed as a MelleaTool and has all the same properties?

jakelorocco · 2026-02-02T14:28:18Z

mellea/backends/tools.py

+            # Extract MelleaTool from decorated functions
+            if hasattr(tool_instance, "_mellea_tool"):
+                tool_instance = tool_instance._mellea_tool


Same as above.

akihikokuroda · 2026-02-02T16:23:52Z

@jakelorocco Thanks for review. I think all comments are addressed.

jakelorocco · 2026-02-03T16:31:03Z

mellea/backends/tools.py

+def tool(
+    func: Callable | None = None, *, name: str | None = None
+) -> MelleaTool | Callable[[Callable], MelleaTool]:


This doesn't work because of your typing. If you do something like:

@tool def tooling(): ... tooling()

You get type hinting errors on tooling() since it thinks it's a regular MelleaTool. For now, I think we should just return a regular MelleaTool and force it to be called with <tool>.run() like the other tools created from from_callable. If users get annoyed, we can add this functionality here.

I made changes. Thanks.

jakelorocco

Sorry, I think I missed this in the last review or the overloading changed it. I think after this change we should be good. Thank you!

jakelorocco · 2026-02-04T14:18:36Z

mellea/backends/tools.py

+@overload
+def tool(func: Callable) -> MelleaTool: ...


Can we add , *, name: str | None = None to this function definition so that you can still change the tool name when you call it on a function directly:

def new_tool(): ... differently_named_tool = tool(new_tool, name="different_name")

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

akihikokuroda requested review from HendrikStrobelt and jakelorocco January 30, 2026 15:53

nrfulton removed the request for review from HendrikStrobelt January 31, 2026 00:20

jakelorocco reviewed Feb 2, 2026

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akihikokuroda force-pushed the issue382 branch from 97edda8 to cb4bad7 Compare February 2, 2026 16:02

akihikokuroda force-pushed the issue382 branch from cb4bad7 to 5ef0aa8 Compare February 2, 2026 19:38

jakelorocco requested changes Feb 3, 2026

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akihikokuroda force-pushed the issue382 branch from 6f88ce1 to 5ebc020 Compare February 4, 2026 00:43

jakelorocco reviewed Feb 4, 2026

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akihikokuroda force-pushed the issue382 branch from 9b9503a to 17af033 Compare February 4, 2026 18:20

akihikokuroda added 6 commits February 4, 2026 13:49

add tool decorator

e846668

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

review comments

9c0fda4

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

fix merge error

4d384e6

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

fix lint error

e564cdb

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

review comments

86440b4

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

review comment

4095165

Signed-off-by: Akihiko Kuroda <akihikokuroda2020@gmail.com>

akihikokuroda force-pushed the issue382 branch from 17af033 to 4095165 Compare February 4, 2026 18:50

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feat: add tool decorator#387

feat: add tool decorator#387
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		# Before the decorator, you had to do:
		# tools = [MelleaTool.from_callable(get_weather), MelleaTool.from_callable(search_web)]

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Misc PR

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akihikokuroda commented Jan 30, 2026 •

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