feat: rec attrset

evaluator/nixjit_builtins/src/lib.rs

@@ -27,11 +27,28 @@ pub mod builtins {
         })
     }
 
-    pub fn import<Ctx: BuiltinsContext>(ctx: &mut Ctx, path: Value) -> Result<Value> {
+    pub fn import(ctx: &mut impl BuiltinsContext, path: Value) -> Result<Value> {
         todo!()
     }
 
     fn elem_at(list: Value, idx: Value) -> Result<Value> {
+        let list = list
+            .try_unwrap_list()
+            .map_err(|_| Error::EvalError("expected a list but found ...".to_string()))?;
+        let idx = idx
+            .try_unwrap_int()
+            .map_err(|_| Error::EvalError("expected a int but found ...".to_string()))?;
+        list.get(idx as usize)
+            .ok_or_else(|| {
+                Error::EvalError(format!(
+                    "'builtins.elemAt' called with index {idx} on a list of size {}",
+                    list.len()
+                ))
+            })
+            .cloned()
+    }
+
+    fn elem(elem: Value, list: Value) -> Result<Value> {
         todo!()
     }
 }