Scope?

src/lib.rs

@@ -1 +1,2 @@
+pub mod scope;
 pub mod types;

src/scope.rs

@@ -0,0 +1,63 @@
+use std::{
+	cell::RefCell,
+	collections::{hash_map::Entry, HashMap},
+	rc::Rc,
+};
+
+use crate::types::Value;
+
+#[derive(Debug, Clone, Default)]
+pub struct Variable(Rc<RefCell<Value>>);
+
+impl Variable {
+	pub fn get(&self) -> Value {
+		self.0.borrow().clone()
+	}
+
+	pub fn set(&self, value: Value) {
+		*self.0.borrow_mut() = value;
+	}
+}
+
+#[derive(Debug, Clone, Default)]
+struct ScopeInner {
+	parent: Option<Scope>,
+	locals: HashMap<String, Variable>,
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct Scope(Rc<RefCell<ScopeInner>>);
+
+impl Scope {
+	pub fn new() -> Self {
+		Self::default()
+	}
+
+	pub fn nested(&self) -> Self {
+		Self(Rc::new(RefCell::new(ScopeInner {
+			parent: Some(self.clone()),
+			..Default::default()
+		})))
+	}
+
+	pub fn add(&self, name: String) {
+		self.0.borrow_mut().locals.insert(name, Variable::default());
+	}
+
+	pub fn get(&self, name: String) -> Variable {
+		let mut this = self.0.borrow_mut();
+		let parent = this.parent.clone();
+		match this.locals.entry(name) {
+			Entry::Occupied(var) => var.get().clone(),
+			Entry::Vacant(var) => {
+				if let Some(parent) = parent {
+					let name = var.into_key();
+					drop(this);
+					parent.get(name)
+				} else {
+					var.insert(Variable::default()).clone()
+				}
+			}
+		}
+	}
+}