diff --git a/control.go b/control.go
index 165a7dc..1c4edeb 100644
--- a/control.go
+++ b/control.go
@@ -11,6 +11,7 @@ const (
 	ControlBoolShortcut  = "_bool_shortcut"
 	ControlSearchPath    = "_search_path"
 	ControlParentContext = "_parent_context"
+	ControlStdout        = "_stdout"
 )
 
 // Other control variables
@@ -23,11 +24,17 @@ const (
 	init_search_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
 )
 
+func SetCtrl(ctx ExprContext, name string, value any) (current any) {
+	current, _ = ctx.GetVar(name)
+	ctx.UnsafeSetVar(name, value)
+	return
+}
+
 func initDefaultVars(ctx ExprContext) {
 	if _, exists := ctx.GetVar(ControlPreset); exists {
 		return
 	}
-	ctx.SetVar(ControlPreset, true)
-	ctx.SetVar(ControlBoolShortcut, true)
-	ctx.SetVar(ControlSearchPath, init_search_path)
+	ctx.UnsafeSetVar(ControlPreset, true)
+	ctx.UnsafeSetVar(ControlBoolShortcut, true)
+	ctx.UnsafeSetVar(ControlSearchPath, init_search_path)
 }