From d7fe17338035c7a15549ec53191650ca95939af3 Mon Sep 17 00:00:00 2001
From: Youngbin Kim <64558592+youngbinkim0@users.noreply.github.com>
Date: Wed, 12 Nov 2025 16:32:20 -0500
Subject: [PATCH] Add FieldwiseChainOfThought predictor class

Introduces the FieldwiseChainOfThought class, which extends Predict to prepend reasoning fields before each output field in a signature. Includes logic for signature extension, state dumping/loading, and activation control to support step-by-step reasoning for model outputs.
---
 dspy/predict/fieldwise_chain_of_thought.py | 81 ++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 dspy/predict/fieldwise_chain_of_thought.py

diff --git a/dspy/predict/fieldwise_chain_of_thought.py b/dspy/predict/fieldwise_chain_of_thought.py
new file mode 100644
index 0000000000..2ccf776a30
--- /dev/null
+++ b/dspy/predict/fieldwise_chain_of_thought.py
@@ -0,0 +1,81 @@
+import dspy.dsp as dsp
+import dspy
+from dspy.signatures.signature import ensure_signature
+from dspy.predict import Predict
+
+class FieldwiseChainOfThought(Predict):
+    def __init__(self, signature, activated=True, **config):
+        super().__init__(signature, **config)
+        self.activated = activated
+        
+        signature = ensure_signature(self.signature)
+        
+        # Build extended signature by prepending reasoning field before each output field
+        extended_signature = signature
+        output_fields = list(signature.output_fields.keys())
+        
+        # Insert reasoning fields in reverse order to maintain correct positions
+        for i, field_name in enumerate(reversed(output_fields)):
+            reasoning_field_name = f"{field_name}_reasoning"
+            reasoning_field = dspy.OutputField(
+                prefix=f"Reasoning for {field_name}: Let's think step by step in order to",
+                desc="${produce the " + field_name + "}. We ...",
+            )
+            # Insert reasoning field right before the output field
+            # Position: negative index from end, accounting for fields we haven't processed yet
+            position = -(len(output_fields) - i)
+            extended_signature = extended_signature.insert(
+                position,
+                reasoning_field_name,
+                reasoning_field,
+                type_=str
+            )
+        
+        self.extended_signature = extended_signature
+
+    def forward(self, **kwargs):
+        new_signature = kwargs.pop("new_signature", None)
+        
+        if new_signature is None:
+            if self.activated is True or (
+                self.activated is None and isinstance(dsp.settings.lm, dsp.GPT3)
+            ):
+                signature = self.extended_signature
+            else:
+                signature = self.signature
+        else:
+            signature = new_signature
+        
+        return super().forward(signature=signature, **kwargs)
+
+    def dump_state(self):
+        state = super().dump_state()
+        
+        # Cache the extended signature instructions
+        state["extended_signature_instructions"] = self.extended_signature.instructions
+        
+        # Cache prefixes for all reasoning fields
+        state["reasoning_field_prefixes"] = {}
+        output_fields = list(self.signature.output_fields.keys())
+        for field_name in output_fields:
+            reasoning_field_name = f"{field_name}_reasoning"
+            if reasoning_field_name in self.extended_signature.fields:
+                state["reasoning_field_prefixes"][reasoning_field_name] = (
+                    self.extended_signature.fields[reasoning_field_name].json_schema_extra['prefix']
+                )
+        
+        return state
+
+    def load_state(self, state):
+        super().load_state(state)
+        
+        # Reconstruct the signature
+        if "extended_signature_instructions" in state:
+            instructions = state["extended_signature_instructions"]
+            self.extended_signature = self.extended_signature.with_instructions(instructions)
+        
+        if "reasoning_field_prefixes" in state:
+            for field_name, prefix in state["reasoning_field_prefixes"].items():
+                self.extended_signature = self.extended_signature.with_updated_fields(
+                    field_name, prefix=prefix
+                )
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