Introduce lf.call as a convenient helper for directly invoking `lf.…

…LangFunc` with possible structured output.

Usage:
```
lf.call('Compute one plus one', lm=lf.llms.Gpt35())
# Returns "two".

lf.call('Compute one plus one', int, lm=lf.llms.Gpt35())
# Returns 2.
```

PiperOrigin-RevId: 569859168

langfun/core/__init__.py

@@ -27,6 +27,9 @@
 from langfun.core.template import Template
 from langfun.core.langfunc import LangFunc
 
+# Function for convenient call LM with possible structured output.
+from langfun.core.langfunc import call
+
 # Decorator for set the positional init args for component.
 from langfun.core.component import use_init_args
 

langfun/core/langfunc.py

@@ -509,3 +509,33 @@ class LangFuncCallEvent(subscription.Event[LangFunc]):
   lm_input: message_lib.Message
   lm_output: message_lib.Message
   lm_callstack: list[LangFunc]
+
+
+def call(prompt: str, returns: Any = None, **kwargs) -> Any:
+  """Call a language model with prompt and formulate response in return type.
+
+  Examples::
+
+    lf.call('Compute one plus one', lm=lf.llms.Gpt35())
+    # Returns "two".
+
+    lf.call('Compute one plus one', int, lm=lf.llms.Gpt35())
+    # Returns 2.
+
+  Args:
+    prompt: User prompt that will be sent to LM, which could be a string or a
+      string template whose variables are provided from **kwargs.
+    returns: Type annotations for return type. If None, the raw LM response will
+      be returned (str). Otherwise, the response will be parsed based on the
+      return type.
+    **kwargs: Keyword arguments. Including options that control the calling
+      behavior, such as `lm`, `temperature`, etc. As well as variables that will
+      be fed to the prompt if it's a string template.
+
+  Returns:
+    A string if `returns` is None or an instance of the return type.
+  """
+  message = LangFunc(prompt, returns=returns)(**kwargs)
+  if returns is None:
+    return message.text
+  return message.result

langfun/core/langfunc_test.py

@@ -19,9 +19,12 @@
 from langfun.core import message
 from langfun.core import message_transform
 from langfun.core import subscription
+from langfun.core.langfunc import call
 from langfun.core.langfunc import LangFunc
 from langfun.core.langfunc import LangFuncCallEvent
 from langfun.core.llms import fake
+# Enables as_structured() operation of LangFunc.
+from langfun.core.structured import parsing  # pylint: disable=unused-import
 import pyglove as pg
 
 
@@ -69,7 +72,7 @@ def test_cached_lm_input_and_output(self):
       self.assertEqual(l.lm_output, 'Hello!!!')
 
 
-class CallTest(unittest.TestCase):
+class LangFuncCallTest(unittest.TestCase):
 
   def test_call(self):
     l = LangFunc('Hello', lm=ExcitedEchoer())
@@ -238,32 +241,21 @@ def test_call_with_overriden_lm_input(self):
       self.assertEqual(t(lm_input=message.UserMessage('Hi')), 'Hi!!!')
 
   def test_call_with_structured_output(self):
-
-    class FakeParseStructured(message_transform.MessageTransform):
-
-      def _transform_path(self, unused_message, input_path, value):
-        return int(str(value))
-
-    prev_as_structured = message_transform.MessageTransform.as_structured
-    message_transform.MessageTransform.as_structured = (
-        lambda self, *args: self >> FakeParseStructured())
-
     l = LangFunc('Compute 1 + 2', returns=int)
-    with component.context(lm=fake.StaticMapping({
-        'Compute 1 + 2': '3',
-    })):
+    with component.context(lm=fake.StaticSequence([
+        'three', '3'
+    ])):
       r = l()
       self.assertEqual(r.result, 3)
 
     l = LangFunc('Compute 1 + 2', returns=int, output_transform=lambda x: '3')
     with component.context(
-        lm=fake.StaticMapping({
-            'Compute 1 + 2': 'three',
-        })
+        lm=fake.StaticSequence([
+            'three', '3'
+        ])
     ):
       r = l()
       self.assertEqual(r.result, 3)
-    message_transform.MessageTransform.as_structured = prev_as_structured
 
 
 class TransformTest(unittest.TestCase):
@@ -379,5 +371,16 @@ def on_event(self, event: LangFuncCallEvent):
     )
 
 
+class CallTest(unittest.TestCase):
+
+  def test_call(self):
+    with component.context(lm=fake.StaticSequence(['three'])):
+      self.assertEqual(call('Compute 1 + 1'), 'three')
+
+  def test_call_with_returns(self):
+    with component.context(lm=fake.StaticSequence(['three', '3'])):
+      self.assertEqual(call('Compute 1 + 1', returns=int), 3)
+
+
 if __name__ == '__main__':
   unittest.main()