Adds as_chat_history

We should move this helper into `Context` in a future sprint.

Author: nrfulton

mellea/stdlib/base.py

@@ -340,6 +340,9 @@ def linearize(self) -> list[Component | CBlock] | None:
         return self._ctx
 
     def is_chat_history(self):
+        FancyLogger.get_logger().warning(
+            "is_chat_history doesn't work properly, because ModelOutputThunks are not Messages."
+        )
         """Returns true if everything in the LinearContext is a chat `Message`."""
         return all(
             str(type(x)) == "Message" for x in self._ctx

mellea/stdlib/chat.py

@@ -3,7 +3,15 @@
 from collections.abc import Mapping
 from typing import Any, Literal
 
-from mellea.stdlib.base import Component, ModelToolCall, TemplateRepresentation
+from mellea.helpers.fancy_logger import FancyLogger
+from mellea.stdlib.base import (
+    CBlock,
+    Component,
+    Context,
+    ModelOutputThunk,
+    ModelToolCall,
+    TemplateRepresentation,
+)
 
 
 class Message(Component):
@@ -85,3 +93,28 @@ def format_for_llm(self) -> TemplateRepresentation:
     def __str__(self):
         """Pretty representation of messages, because they are a special case."""
         return f'mellea.Message(role="{self.role}", content="{self.content}", name="{self.name}")'
+
+
+def as_chat_history(ctx: Context) -> list[Message]:
+    """Returns a list of Messages corresponding to a Context."""
+
+    def _to_msg(c: CBlock | Component | ModelOutputThunk) -> Message | None:
+        match c:
+            case Message():
+                return c
+            case ModelOutputThunk():
+                match c.parsed_repr:
+                    case Message():
+                        return c.parsed_repr
+                    case _:
+                        return None
+            case _:
+                return None
+
+    linearized_ctx = ctx.linearize()
+    if linearized_ctx is None:
+        raise Exception("Trying to cast a non-linear history into a chat history.")
+    else:
+        history = [_to_msg(c) for c in linearized_ctx]
+        assert None not in history, "Could not render this context as a chat history."
+        return history  # type: ignore

test/stdlib_basics/test_chat_view.py

@@ -0,0 +1,23 @@
+import pytest
+from mellea.stdlib.base import ModelOutputThunk, LinearContext
+from mellea.stdlib.chat import as_chat_history, Message
+from mellea.stdlib.session import start_session
+
+
+def test_chat_view_linear_ctx():
+    m = start_session(ctx=LinearContext())
+    m.chat("What is 1+1?")
+    m.chat("What is 2+2?")
+    assert len(as_chat_history(m.ctx)) == 4
+    assert all([type(x) == Message for x in as_chat_history(m.ctx)])
+
+@pytest.mark.skip("linearize() returns [] for a SimpleContext... that's going to be annoying.")
+def test_chat_view_simple_ctx():
+    m = start_session()
+    m.chat("What is 1+1?")
+    m.chat("What is 2+2?")
+    assert len(as_chat_history(m.ctx)) == 2
+    assert all([type(x) == Message for x in as_chat_history(m.ctx)])
+
+if __name__ == "__main__":
+    pytest.main([__file__])