Enhance error handling

trans/transpiler/phases/typing/block.py

@@ -8,6 +8,7 @@ from transpiler.phases.typing.class_ import ScoperClassVisitor
 from transpiler.phases.typing.scope import VarDecl, VarKind, ScopeKind
 from transpiler.phases.typing.types import BaseType, TypeVariable, FunctionType, IncompatibleTypesError, \
     Promise, TY_NONE, PromiseKind, TupleType, UserType, TypeType, ModuleType
+from transpiler.phases.utils import PlainBlock
 
 
 @dataclass
@@ -23,6 +24,9 @@ class ScoperBlockVisitor(ScoperVisitor):
     def visit_Import(self, node: ast.Import):
         for alias in node.names:
             mod = self.scope.get(alias.name, VarKind.MODULE)
+            if mod is None:
+                raise NameError(alias.name)
+            assert isinstance(mod, VarDecl), mod
             self.scope.vars[alias.asname or alias.name] = dataclasses.replace(mod, kind=VarKind.LOCAL)
 
     def visit_ImportFrom(self, node: ast.ImportFrom):
@@ -174,7 +178,7 @@ class ScoperBlockVisitor(ScoperVisitor):
         try:
             iter_type = seq_type.methods["__iter__"].return_type
         except:
-            raise IncompatibleTypesError(f"{seq_type} is not iterable")
+            raise IncompatibleTypesError(f"{seq_type} is not iterable in `{ast.unparse(node.iter)}`")
         try:
             next_type = iter_type.methods["__next__"].return_type
         except: