UI: Factor out UI components into a library; require 'use UI' for activation

Author: ProgrammerKR

examples/ui_test.prox

@@ -1,3 +1,5 @@
+use UI;
+
 App MyLibraryApp {
     State count = 0;
 

include/parser.h

@@ -19,6 +19,7 @@ typedef struct {
   int current;
   bool panicMode;
   bool hadError;
+  bool uiEnabled;
   const char *source;
 } Parser;
 

src/compiler/parser/parser.c

@@ -95,6 +95,7 @@ void initParser(Parser *parser, Token *tokens, int count, const char *source) {
   parser->current = 0;
   parser->panicMode = false;
   parser->hadError = false;
+  parser->uiEnabled = false;
   parser->source = source;
 }
 
@@ -610,6 +611,7 @@ static Stmt *useDecl(Parser *p) {
     }
 
     appendString(modules, path);
+    if (strcmp(path, "UI") == 0) p->uiEnabled = true;
   } while (match(p, 1, TOKEN_COMMA));
 
   consume(p, TOKEN_SEMICOLON, "Expect ';'.");
@@ -733,6 +735,11 @@ static Stmt *statement(Parser *p) {
     }
 
     // UI Declarations
+    if (check(p, TOKEN_UI_APP) || check(p, TOKEN_UI_WINDOW)) {
+        if (!p->uiEnabled) {
+            parserError(p, "UI components require 'use UI' to be imported.");
+        }
+    }
     if (match(p, 1, TOKEN_UI_APP)) return uiAppDecl(p);
     if (match(p, 1, TOKEN_UI_WINDOW)) return uiWindowDecl(p);
     if (match(p, 1, TOKEN_UI_STATE)) return uiStateDecl(p);

std/lib/ui.prox

@@ -0,0 +1,9 @@
+// --------------------------------------------------
+//   Project: ProX Programming Language (ProXPL)
+//   Author:  ProgrammerKR
+//   Created: 2026-02-26
+//   Description: UI Library marker file.
+// --------------------------------------------------
+
+// This file serves as a marker for the built-in UI library.
+// Importing this library enables UI keywords and components.