feat: init

src/vm/env.rs

@@ -0,0 +1,47 @@
+use rpds::HashTrieMapSync;
+
+use super::value::{Symbol, VmValue};
+
+pub struct Env {
+    last: Option<*mut Env>,
+    map: HashTrieMapSync<Symbol, VmValue>,
+}
+
+impl Env {
+    pub fn empty() -> Env {
+        Env {
+            last: None,
+            map: HashTrieMapSync::new_sync(),
+        }
+    }
+
+    pub fn lookup(&self, symbol: Symbol) -> VmValue {
+        if let Some(value) = self.map.get(&symbol) {
+            value.clone()
+        } else {
+            let last = unsafe { &*self.last.unwrap() };
+            last.lookup(symbol)
+        }
+    }
+
+    pub fn insert(&mut self, symbol: Symbol, value: VmValue) {
+        self.map.insert_mut(symbol, value);
+    }
+
+    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);
+    }
+
+    pub fn leave(&mut self) {
+        let last = unsafe { &*self.last.unwrap() };
+        self.last = last.last;
+        self.map = last.map.clone();
+    }
+}