I can apply format rules

src/myfasthtml/core/formatting/condition_evaluator.py

@@ -1,3 +1,4 @@
+from numbers import Number
 from typing import Any
 
 from myfasthtml.core.formatting.dataclasses import Condition
@@ -32,6 +33,10 @@ class ConditionEvaluator:
         if condition.operator == "isnotempty":
             result = not self._is_empty(cell_value)
             return self._apply_negate(result, condition.negate)
+        
+        if condition.operator == "isnan":
+            result = self._is_nan(cell_value)
+            return self._apply_negate(result, condition.negate)
 
         # For all other operators, None cell_value returns False
         if cell_value is None:
@@ -70,6 +75,10 @@ class ConditionEvaluator:
         if isinstance(value, str) and value == "":
             return True
         return False
+    
+    def _is_nan(self, value: Any) -> bool:
+        """Check if a value is NaN."""
+        return isinstance(value, float) and value != value
 
     def _apply_negate(self, result: bool, negate: bool) -> bool:
         """Apply negation if needed."""
@@ -124,7 +133,7 @@ class ConditionEvaluator:
         """Check if cell_value < compare_value."""
         if type(cell_value) != type(compare_value):
             # Allow int/float comparison
-            if isinstance(cell_value, (int, float)) and isinstance(compare_value, (int, float)):
+            if isinstance(cell_value, Number) and isinstance(compare_value, Number):
                 return cell_value < compare_value
             raise TypeError("Type mismatch")
         return cell_value < compare_value
@@ -132,7 +141,7 @@ class ConditionEvaluator:
     def _less_than_or_equal(self, cell_value: Any, compare_value: Any) -> bool:
         """Check if cell_value <= compare_value."""
         if type(cell_value) != type(compare_value):
-            if isinstance(cell_value, (int, float)) and isinstance(compare_value, (int, float)):
+            if isinstance(cell_value, Number) and isinstance(compare_value, Number):
                 return cell_value <= compare_value
             raise TypeError("Type mismatch")
         return cell_value <= compare_value
@@ -140,7 +149,7 @@ class ConditionEvaluator:
     def _greater_than(self, cell_value: Any, compare_value: Any) -> bool:
         """Check if cell_value > compare_value."""
         if type(cell_value) != type(compare_value):
-            if isinstance(cell_value, (int, float)) and isinstance(compare_value, (int, float)):
+            if isinstance(cell_value, Number) and isinstance(compare_value, Number):
                 return cell_value > compare_value
             raise TypeError("Type mismatch")
         return cell_value > compare_value
@@ -148,7 +157,7 @@ class ConditionEvaluator:
     def _greater_than_or_equal(self, cell_value: Any, compare_value: Any) -> bool:
         """Check if cell_value >= compare_value."""
         if type(cell_value) != type(compare_value):
-            if isinstance(cell_value, (int, float)) and isinstance(compare_value, (int, float)):
+            if isinstance(cell_value, Number) and isinstance(compare_value, Number):
                 return cell_value >= compare_value
             raise TypeError("Type mismatch")
         return cell_value >= compare_value

src/myfasthtml/core/formatting/dataclasses.py

@@ -121,6 +121,9 @@ class TextFormatter(Formatter):
     max_length: int = None
     ellipsis: str = "..."
 
+@dataclass
+class ConstantFormatter(Formatter):
+    value: str = None
 
 @dataclass
 class EnumFormatter(Formatter):

src/myfasthtml/core/formatting/formatter_resolver.py

@@ -9,6 +9,7 @@ from myfasthtml.core.formatting.dataclasses import (
     BooleanFormatter,
     TextFormatter,
     EnumFormatter,
+    ConstantFormatter,
 )
 from myfasthtml.core.formatting.presets import DEFAULT_FORMATTER_PRESETS
 
@@ -258,6 +259,15 @@ class EnumFormatterResolver(BaseFormatterResolver):
             )
 
 
+class ConstantFormatterResolver(BaseFormatterResolver):
+    
+    def resolve(self, formatter: ConstantFormatter, value: Any) -> str:
+        return formatter.value
+    
+    def apply_preset(self, formatter: Formatter, presets: dict) -> Formatter:
+        return formatter
+
+
 class FormatterResolver:
     """
     Main resolver that dispatches to the appropriate formatter resolver.
@@ -281,6 +291,7 @@ class FormatterResolver:
             BooleanFormatter: BooleanFormatterResolver(),
             TextFormatter: TextFormatterResolver(),
             EnumFormatter: EnumFormatterResolver(lookup_resolver),
+            ConstantFormatter: ConstantFormatterResolver()
         }
 
     def resolve(self, formatter: Formatter, value: Any) -> str: