feat: add monkey-rs

__lang/monkey-rs/src/environment.rs

@@ -0,0 +1,37 @@
+use crate::object::Object;
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::rc::Rc;
+
+#[derive(Debug, PartialEq, Default)]
+pub struct Environment {
+    store: HashMap<String, Object>,
+    outer: Option<Rc<RefCell<Environment>>>,
+}
+
+impl Environment {
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    pub fn extend(outer: Rc<RefCell<Self>>) -> Environment {
+        Environment {
+            store: HashMap::new(),
+            outer: Some(outer),
+        }
+    }
+
+    pub fn get(&self, name: &str) -> Option<Object> {
+        match self.store.get(name) {
+            Some(value) => Some(value.clone()),
+            None => self
+                .outer
+                .as_ref()
+                .and_then(|o| o.borrow().get(name).clone()),
+        }
+    }
+
+    pub fn set(&mut self, name: &str, val: Object) {
+        self.store.insert(name.to_string(), val);
+    }
+}