Initialize Aster project with basic structure, including Cargo configuration, lexer, parser, interpreter, and AST definitions. Add a sample script and README documentation. Implement basic error handling and environment management for variable storage.

src/interpreter/env.rs

@@ -0,0 +1,44 @@
+use super::Value;
+use std::collections::HashMap;
+use std::rc::Rc;
+use std::cell::RefCell;
+
+#[derive(Debug)]
+pub struct Env {
+    pub values: HashMap<String, Value>,
+    pub parent: Option<Rc<RefCell<Env>>>,
+}
+
+impl Env {
+    pub fn new(parent: Option<Rc<RefCell<Env>>>) -> Self {
+        Self {
+            values: HashMap::new(),
+            parent,
+        }
+    }
+
+    pub fn define(&mut self, name: String, val: Value) {
+        self.values.insert(name, val);
+    }
+
+    pub fn assign(&mut self, name: &str, val: Value) -> bool {
+        if self.values.contains_key(name) {
+            self.values.insert(name.to_string(), val);
+            true
+        } else if let Some(parent) = &self.parent {
+            parent.borrow_mut().assign(name, val)
+        } else {
+            false
+        }
+    }
+
+    pub fn get(&self, name: &str) -> Option<Value> {
+        if let Some(val) = self.values.get(name) {
+            Some(val.clone())
+        } else if let Some(parent) = &self.parent {
+            parent.borrow().get(name)
+        } else {
+            None
+        }
+    }
+}