feat: refactor

src/vm/env.rs

@@ -3,7 +3,7 @@ use rpds::HashTrieMapSync;
 use super::value::{Symbol, VmValue};
 
 pub struct Env {
-    last: Option<*mut Env>,
+    last: Option<Box<Env>>,
     map: HashTrieMapSync<Symbol, VmValue>,
 }
 
@@ -19,7 +19,7 @@ impl Env {
         if let Some(value) = self.map.get(&symbol) {
             value.clone()
         } else {
-            let last = unsafe { &*self.last.unwrap() };
+            let last = self.last.as_ref().unwrap();
             last.lookup(symbol)
         }
     }
@@ -29,19 +29,13 @@ impl Env {
     }
 
     pub fn enter(&mut self, map: HashTrieMapSync<Symbol, VmValue>) {
-        let last = std::mem::replace(
-            self,
-            Env {
-                last: None,
-                map,
-            },
-        );
-        self.last = Some(Box::leak(Box::new(last)) as *mut Env);
+        let last = std::mem::replace(self, Env { last: None, map });
+        self.last = Some(Box::new(last));
     }
 
     pub fn leave(&mut self) {
-        let last = unsafe { &*self.last.unwrap() };
-        self.last = last.last;
+        let last = std::mem::replace(&mut self.last, None).unwrap();
+        let _ = std::mem::replace(&mut self.last, last.last);
         self.map = last.map.clone();
     }
 }