Feature: ftd.ui variable reference

ftd/src/interpreter2/things/value.rs

@@ -362,10 +362,22 @@ impl PropertyValue {
         value: ftd::ast::VariableValue,
         doc: &mut ftd::interpreter2::TDoc,
         definition_name_with_arguments: Option<(&str, &[ftd::interpreter2::Argument])>,
+        loop_object_name_and_kind: &Option<(String, ftd::interpreter2::Argument)>,
     ) -> ftd::interpreter2::Result<
         ftd::interpreter2::StateWithThing<ftd::interpreter2::PropertyValue>,
     > {
         let line_number = value.line_number();
+
+        if key.eq("ftd.ui") {
+            return ftd::interpreter2::PropertyValue::from_ast_value_with_argument(
+                value,
+                doc,
+                false,
+                Some(&ftd::interpreter2::Kind::ui().into_kind_data()),
+                definition_name_with_arguments,
+                loop_object_name_and_kind,
+            );
+        }
         let ast_component = ftd::ast::Component::from_variable_value(key, value, doc.name)?;
         let component = try_ok_state!(ftd::interpreter2::Component::from_ast_component(
             ast_component,
@@ -779,6 +791,7 @@ impl PropertyValue {
                                 value,
                                 doc,
                                 definition_name_with_arguments,
+                                loop_object_name_and_kind
                             )?)
                         } else {
                             try_ok_state!(PropertyValue::from_ast_value(
@@ -1608,6 +1621,21 @@ impl Value {
         }
     }
 
+    pub fn ui(
+        &self,
+        doc_id: &str,
+        line_number: usize,
+    ) -> ftd::interpreter2::Result<ftd::interpreter2::Component> {
+        match self {
+            ftd::interpreter2::Value::UI { component, .. } => Ok(component.to_owned()),
+            t => ftd::interpreter2::utils::e2(
+                format!("Expected UI, found: `{:?}`", t),
+                doc_id,
+                line_number,
+            ),
+        }
+    }
+
     pub fn optional_string(
         &self,
         doc_id: &str,

ftd/t/html/75-ui-list-display.ftd

@@ -0,0 +1,18 @@
+-- ftd.ui list uis:
+
+-- ftd.text: Hello
+
+-- ftd.column:
+-- ftd.text: Column Hello
+-- end: ftd.column
+
+-- end: uis
+
+
+-- ftd.column:
+-- ftd.column.children:
+
+-- ftd.ui: $uis.1
+
+-- end: ftd.column.children
+-- end: ftd.column