remove map_foreign from Mapper

Author: majosm

pytato/stringifier.py

@@ -39,7 +39,7 @@
     IndexLambda,
     ReductionDescriptor,
 )
-from pytato.transform import Mapper
+from pytato.transform import ForeignObjectError, Mapper
 
 
 if TYPE_CHECKING:
@@ -77,7 +77,10 @@ def rec(self, expr: Any, depth: int) -> str:
         try:
             return self._cache[cache_key]
         except KeyError:
-            result = super().rec(expr, depth)
+            try:
+                result = super().rec(expr, depth)
+            except ForeignObjectError:
+                result = self.map_foreign(expr, depth)
             self._cache[cache_key] = result
             return result
 

pytato/transform/__init__.py

@@ -161,6 +161,10 @@ class UnsupportedArrayError(ValueError):
     pass
 
 
+class ForeignObjectError(ValueError):
+    pass
+
+
 # {{{ mapper base class
 
 ResultT = TypeVar("ResultT")
@@ -199,13 +203,6 @@ def handle_unsupported_array(self, expr: MappedT,
         raise UnsupportedArrayError(
                 f"{type(self).__name__} cannot handle expressions of type {type(expr)}")
 
-    def map_foreign(self, expr: Any, *args: P.args, **kwargs: P.kwargs) -> Any:
-        """Mapper method that is invoked for an object of class for which a
-        mapper method does not exist in this mapper.
-        """
-        raise ValueError(
-                f"{type(self).__name__} encountered invalid foreign object: {expr!r}")
-
     def rec(self, expr: ArrayOrNames, *args: P.args, **kwargs: P.kwargs) -> ResultT:
         """Call the mapper method of *expr* and return the result."""
         method: Callable[..., Any] | None
@@ -223,7 +220,9 @@ def rec(self, expr: ArrayOrNames, *args: P.args, **kwargs: P.kwargs) -> ResultT:
                 else:
                     return self.handle_unsupported_array(expr, *args, **kwargs)
             else:
-                return cast("ResultT", self.map_foreign(expr, *args, **kwargs))
+                raise ForeignObjectError(
+                    f"{type(self).__name__} encountered invalid foreign "
+                    f"object: {expr!r}") from None
 
         assert method is not None
         return cast("ResultT", method(expr, *args, **kwargs))
@@ -237,7 +236,8 @@ def rec_function_definition(
         try:
             method = self.map_function_definition  # type: ignore[attr-defined]
         except AttributeError:
-            return cast("FunctionResultT", self.map_foreign(expr, *args, **kwargs))
+            raise ValueError(
+                f"{type(self).__name__} lacks a mapper method for functions.") from None
 
         assert method is not None
         return cast("FunctionResultT", method(expr, *args, **kwargs))