From bd37163138ea328b27d4340777bc9853160a16c3 Mon Sep 17 00:00:00 2001
From: Manmohan Sharma <manmohan659@gmail.com>
Date: Wed, 22 Apr 2026 16:04:26 -0700
Subject: [PATCH] fix: auto-inject calculator tool call on arithmetic in user
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needs_calculator now extracts the actual expression from: bare arithmetic (900+100), verbal math (900 plus 100), percentage (17% tip on 45), with comma-stripping and whitespace normalization. serve.py wires it into the force-prefix path parallel to web_search — if no web-search trigger, check calculator, pre-seed real tool call + result so the model sees the grounded answer in context.
---
 modal/_query_classifier.py | 54 ++++++++++++++++++++++++++++----------
 modal/serve.py             | 27 ++++++++++++++++++-
 2 files changed, 66 insertions(+), 15 deletions(-)

diff --git a/modal/_query_classifier.py b/modal/_query_classifier.py
index 1146d815..555ecd76 100644
--- a/modal/_query_classifier.py
+++ b/modal/_query_classifier.py
@@ -386,23 +386,49 @@ def _rewrite_query(text: str) -> str:
 # Calculator triggers (cheap, local)
 # ---------------------------------------------------------------------------
 
-_CALC_RX = re.compile(
-    r"""
-    \b(?:calculate|compute|what\s+is|what's)\b.*?
-    (?:
-      \d[\d,\.\s]*\s*[+\-\*/x×÷]\s*\d               # basic arithmetic
-    | \d+\s*%\s+(?:of|tip|tax|discount)\s+\d        # percentage
-    | \b(?:emi|cagr|compound\s+interest|tip|discount|percent(?:age)?)\b.*\d
-    )
-    """,
-    re.IGNORECASE | re.VERBOSE,
+_BARE_EXPR_RX = re.compile(
+    r"(-?\d[\d,\.]*\s*[+\-*/×÷]\s*-?\d[\d,\.]*(?:\s*[+\-*/×÷]\s*-?\d[\d,\.]*)*)"
 )
+_PERCENT_RX = re.compile(
+    r"(\d+(?:\.\d+)?)\s*(?:%|percent)\s+(?:of|tip|tax|discount|off)\s+(?:on\s+)?\$?(\d+(?:\.\d+)?)",
+    re.IGNORECASE,
+)
+_VERBAL_RX = re.compile(
+    r"(\d+(?:\.\d+)?)\s+(plus|minus|times|divided\s+by|multiplied\s+by|over)\s+(\d+(?:\.\d+)?)",
+    re.IGNORECASE,
+)
+_WORD_OP = {
+    "plus": "+", "minus": "-", "times": "*",
+    "multiplied by": "*", "divided by": "/", "over": "/",
+}
+
+
+def _normalize_expr(expr: str) -> str:
+    e = expr.replace(",", "").replace("×", "*").replace("÷", "/")
+    e = re.sub(r"\s+", "", e)  # strip all internal whitespace
+    return e
 
 
 def needs_calculator(text: str) -> Tuple[bool, str]:
+    """Return (True, expression) if the text contains arithmetic that the
+    calculator tool should execute. `expression` is passed as-is to the
+    sandboxed evaluator (accepts +-*/ on numbers, plus helpers like
+    percent(base,rate), emi(p,r,n), cagr(s,e,y))."""
     if not text:
         return False, ""
-    m = _CALC_RX.search(text)
-    if not m:
-        return False, ""
-    return True, text.strip()
+    # 1. percentage phrasing
+    m = _PERCENT_RX.search(text)
+    if m:
+        return True, f"percent({m.group(2)},{m.group(1)})"
+    # 2. verbal arithmetic
+    m = _VERBAL_RX.search(text)
+    if m:
+        op = _WORD_OP[m.group(2).lower().replace("  ", " ").strip()]
+        return True, f"{m.group(1)}{op}{m.group(3)}"
+    # 3. bare arithmetic expression
+    m = _BARE_EXPR_RX.search(text)
+    if m:
+        return True, _normalize_expr(m.group(1))
+    return False, ""
+
+
diff --git a/modal/serve.py b/modal/serve.py
index fb74b6f5..e90cfd5f 100644
--- a/modal/serve.py
+++ b/modal/serve.py
@@ -199,11 +199,12 @@ class Inference:
         import sys as _sys
         if '/root' not in _sys.path: _sys.path.insert(0, '/root')
         from _tools import build_default_tool_registry, parse_tool_call_payload
-        from _query_classifier import needs_web_search, needs_web_search_contextual
+        from _query_classifier import needs_web_search, needs_web_search_contextual, needs_calculator
         self.tool_registry = build_default_tool_registry()
         self._parse_tool_call = parse_tool_call_payload
         self._needs_web_search = needs_web_search
         self._needs_web_search_contextual = needs_web_search_contextual
+        self._needs_calculator = needs_calculator
         # Marker tokens for tool state machine
         self.python_start_id = self.tokenizer.encode_special("<|python_start|>")[0]
         self.python_end_id = self.tokenizer.encode_special("<|python_end|>")[0]
@@ -316,6 +317,30 @@ class Inference:
                 + "<|output_start|>" + result_text + "<|output_end|>\n"
             )
             tokens.extend(self.tokenizer.encode(forced_prefix_text))
+        else:
+            # Try calculator force-inject: arithmetic in the user message?
+            try:
+                needs_calc, calc_expr = self._needs_calculator(query_for_classify)
+            except Exception:
+                needs_calc, calc_expr = False, ""
+            if needs_calc and calc_expr:
+                preface = "Let me calculate that. "
+                calc_call_json = json.dumps(
+                    {"arguments": {"expression": calc_expr}, "tool": "calculator"},
+                    separators=(",", ":"),
+                )
+                try:
+                    invocation = self._parse_tool_call(calc_call_json)
+                    calc_result = self.tool_registry.execute(invocation.tool_name, invocation.arguments)
+                    calc_result_text = calc_result.to_payload()[:2048]
+                except Exception as exc:
+                    calc_result_text = json.dumps({"error": str(exc)[:500]})
+                forced_prefix_text = (
+                    preface
+                    + "<|python_start|>" + calc_call_json + "<|python_end|>"
+                    + "<|output_start|>" + calc_result_text + "<|output_end|>\n"
+                )
+                tokens.extend(self.tokenizer.encode(forced_prefix_text))
 
         # Truncate to fit context
         max_context = self.config.sequence_len - max_tokens