diff --git a/ucl/inst.go b/ucl/inst.go
index 7493338..65f0c90 100644
--- a/ucl/inst.go
+++ b/ucl/inst.go
@@ -73,6 +73,9 @@ func (inst *Inst) Out() io.Writer {
 func (inst *Inst) Eval(ctx context.Context, expr string) (any, error) {
 	res, err := inst.eval(ctx, expr)
 	if err != nil {
+		if errors.Is(err, ErrHalt) {
+			return nil, nil
+		}
 		return nil, err
 	}
 
diff --git a/ucl/objs.go b/ucl/objs.go
index 47bd7cb..bfa3081 100644
--- a/ucl/objs.go
+++ b/ucl/objs.go
@@ -465,3 +465,5 @@ type errReturn struct {
 func (e errReturn) Error() string {
 	return "return"
 }
+
+var ErrHalt = errors.New("halt")