elements in lists are lazy

README.md

@@ -51,8 +51,7 @@ implemented.
 
  - 🌕 stage 0: evaluate basic expressions, rec attrsets, let bindings, `with`
  statement, functions
- - 🌖 stage 1:
- - 🌖 lazy evaluation (missing: lazy evaluation in lists)
+ - 🌕 stage 1: lazy evaluation
  - 🌘 stage 2:
  - 🌘 built-in functions (progress: 1 out of 111)
  - 🌑 derivations (hello world derivation)

src/eval/nix_v8.rs

@@ -331,8 +331,9 @@ fn emit_let_in(let_in: &ast::LetIn, out_src: &mut String) -> Result<(), String>
 fn emit_list(list: &ast::List, out_src: &mut String) -> Result<(), String> {
  *out_src += "new n.NixList([";
  for element in list.items() {
+ out_src.push_str("new n.Lazy(ctx,(ctx) => ");
  emit_expr(&element, out_src)?;
- *out_src += ",";
+ out_src.push_str("),");
  }
  *out_src += "])";
  Ok(())
@@ -1230,4 +1231,9 @@ mod tests {
  fn test_eval_builtin_head() {
  assert_eq!(eval_ok("builtins.head [ 1 2 ]"), Value::Int(1));
  }
+
+ #[test]
+ fn test_eval_lists_are_lazy() {
+ assert_eq!(eval_ok("builtins.head [ 1 (1 / 0) ]"), Value::Int(1));
+ }
 }