chapter 9 in rust

rust/rox/src/environment.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::{cell::RefCell, collections::HashMap, rc::Rc};
 
 use thiserror::Error;
 
@@ -15,14 +15,15 @@ pub enum EnvironmentError {
 #[derive(Default, Debug, Clone)]
 pub struct Environment {
     values: HashMap<String, Value>,
-    enclosing: Option<Box<Environment>>,
+    enclosing: Option<Rc<RefCell<Environment>>>,
 }
 
 impl Environment {
-    pub fn with_enclosing(enclosing: Environment) -> Self {
+    /// Initialize a new environment with an enclosing one.
+    pub fn with_enclosing(enclosing: Rc<RefCell<Environment>>) -> Self {
         Self {
             values: HashMap::default(),
-            enclosing: Some(Box::new(enclosing)),
+            enclosing: Some(enclosing),
         }
     }
 
@@ -40,7 +41,7 @@ impl Environment {
             self.values.insert(token.lexeme.clone(), value);
             Ok(())
         } else if let Some(enclosing) = &mut self.enclosing {
-            enclosing.assign(token, value)
+            enclosing.borrow_mut().assign(token, value)
         } else {
             Err(EnvironmentError::UndefinedVariable(
                 token.line,
@@ -55,7 +56,7 @@ impl Environment {
         if let Some(v) = self.values.get(token.lexeme.as_str()) {
             Ok(v.clone())
         } else if let Some(enclosing) = &self.enclosing {
-            enclosing.get(token)
+            enclosing.borrow().get(token)
         } else {
             Err(EnvironmentError::UndefinedVariable(
                 token.line,