refact: move Exception to its own class

Author: boriel

src/ast/ast.py

@@ -7,10 +7,12 @@
 
 import types
 from collections.abc import Callable
-from typing import Any
+from typing import Any, Final
 
 from .tree import Tree
 
+__all__: Final[tuple[str, ...]] = "Ast", "NodeVisitor"
+
 
 # ----------------------------------------------------------------------
 # Abstract Syntax Tree class
@@ -34,12 +36,13 @@ def visit(self, node):
 
         while stack:
             try:
-                last = stack[-1]
-                if isinstance(last, types.GeneratorType):
-                    stack.append(last.send(last_result))
+                stack_top = stack[-1]
+                if isinstance(stack_top, types.GeneratorType):
+                    stack.append(stack_top.send(last_result))
                     last_result = None
-                elif isinstance(last, self.node_type):
-                    stack.append(self._visit(stack.pop()))
+                elif isinstance(stack_top, self.node_type):
+                    stack.pop()
+                    stack.append(self._visit(stack_top))
                 else:
                     last_result = stack.pop()
             except StopIteration:
@@ -55,7 +58,10 @@ def generic_visit(self, node: Ast):
         raise RuntimeError(f"No visit_{node.token}() method defined")
 
     def filter_inorder(
-        self, node, filter_func: Callable[[Any], bool], child_selector: Callable[[Ast], bool] = lambda x: True
+        self,
+        node,
+        filter_func: Callable[[Any], bool],
+        child_selector: Callable[[Ast], bool] = lambda x: True,
     ):
         """Visit the tree inorder, but only those that return true for filter_func and visiting children which
         return true for child_selector.

src/ast/exceptions.py

@@ -0,0 +1,18 @@
+from typing import Final
+
+from src.api.exception import Error
+
+__all__: Final[tuple[str, ...]] = ("NotAnAstError",)
+
+
+class NotAnAstError(Error):
+    """Thrown when the "pointer" is not
+    an AST, but another thing.
+    """
+
+    def __init__(self, instance):
+        self.instance = instance
+        self.msg = "Object '%s' is not an Ast instance" % str(instance)
+
+    def __str__(self):
+        return self.msg

src/ast/tree.py

@@ -11,22 +11,7 @@
 from collections.abc import Iterable, Iterator
 from typing import Any
 
-from src.api.exception import Error
-
-__all__ = "ChildrenList", "NotAnAstError", "Tree"
-
-
-class NotAnAstError(Error):
-    """Thrown when the "pointer" is not
-    an AST, but another thing.
-    """
-
-    def __init__(self, instance):
-        self.instance = instance
-        self.msg = "Object '%s' is not an Ast instance" % str(instance)
-
-    def __str__(self):
-        return self.msg
+__all__ = "ChildrenList", "Tree"
 
 
 class Tree:

src/zxbasm/expr.py

@@ -7,7 +7,7 @@
 
 from src.api.errmsg import error
 from src.ast import Ast
-from src.ast.tree import NotAnAstError
+from src.ast.exceptions import NotAnAstError
 from src.zxbasm.label import Label