feat(visitor): add VisitorMut trait.

crates/fuse-visitor/src/visitor_mut.rs

@@ -0,0 +1,42 @@
+use crate::{visit, visit_list, visit_scope};
+use fuse_ast::ast::*;
+
+pub trait VisitorMut<'ast>: Sized {
+    fn enter_scope(&mut self) {}
+
+    fn leave_scope(&mut self) {}
+
+    fn visit_chunk(&mut self, chunk: &'ast mut Chunk) {
+        walk_block_mut(self, &mut chunk.body)
+    }
+
+    fn visit_block(&mut self, block: &'ast mut Block) {
+        walk_block_mut(self, block)
+    }
+
+    fn visit_statement_mut(&mut self, statement: &'ast mut Statement) {
+        walk_statement_mut(self, statement)
+    }
+}
+
+pub fn walk_block_mut<'ast, V: VisitorMut<'ast>>(visitor: &mut V, block: &'ast mut Block) {
+    visit_scope!(visitor => {
+        visit_list!(visitor.visit_statement_mut(&mut block.statements));
+    });
+}
+
+pub fn walk_statement_mut<'ast, V: VisitorMut<'ast>>(
+    visitor: &mut V,
+    statement: &'ast mut Statement,
+) {
+    match statement {
+        Statement::Empty(_) => {}
+        // Statement::Expression(expr) => visit!(visitor.visit_expression(expr)),
+        // Statement::VariableDeclaration(decl) => visit!(visitor.visit_variable_declaration(decl)),
+        // Statement::FunctionDeclaration(func) => visit!(visitor.visit_function_declaration(func)),
+        // Statement::EnumDeclaration(decl) => visit!(visitor.visit_enum_declaration(decl)),
+        // Statement::StructDeclaration(Box<StructDeclaration>),
+        // Statement::ImplStatement(Box<ImplStatement>),
+        _ => todo!(),
+    }
+}