1 files changed, 40 insertions, 0 deletions
diff --git a/src/common/env.rs b/src/common/env.rs
new file mode 100644
index 000000000000..8b5cde49e9e4
--- /dev/null
+++ b/src/common/env.rs
@@ -0,0 +1,40 @@
+use std::collections::HashMap;
+
+use crate::ast::Ident;
+
+/// A lexical environment
+#[derive(Debug, PartialEq, Eq)]
+pub struct Env<'ast, V>(Vec<HashMap<&'ast Ident<'ast>, V>>);
+
+impl<'ast, V> Default for Env<'ast, V> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<'ast, V> Env<'ast, V> {
+    pub fn new() -> Self {
+        Self(vec![Default::default()])
+    }
+
+    pub fn push(&mut self) {
+        self.0.push(Default::default());
+    }
+
+    pub fn pop(&mut self) {
+        self.0.pop();
+    }
+
+    pub fn set(&mut self, k: &'ast Ident<'ast>, v: V) {
+        self.0.last_mut().unwrap().insert(k, v);
+    }
+
+    pub fn resolve<'a>(&'a self, k: &'ast Ident<'ast>) -> Option<&'a V> {
+        for ctx in self.0.iter().rev() {
+            if let Some(res) = ctx.get(k) {
+                return Some(res);
+            }
+        }
+        None
+    }
+}