diff --git a/src/ast.rs b/src/ast.rs
index f84c47a..3fede85 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -102,6 +102,11 @@ pub enum ExprKind {
     },
     Not(Box<Expr>),
     Literal(Value),
+    Cart(Vec<(Expr, Expr)>),
+    Index {
+        cart: Box<Expr>,
+        index: Box<Expr>,
+    },
     Variable(String),
 }
 
diff --git a/src/interpret.rs b/src/interpret.rs
index 7318056..888b314 100644
--- a/src/interpret.rs
+++ b/src/interpret.rs
@@ -195,6 +195,7 @@ impl ExecEnv {
             }
             Not(expr) => Bool(!self.eval_expr(&expr)?.into_bool()),
             Literal(value) => value.clone(),
+            Cart(_) | Index { .. } => todo!("cart support"),
 
             // TODO: not too happy with constructing an artificial
             // Iden here.