change ui backends to singletons

extra/ui/cocoa/cocoa.factor

@@ -12,7 +12,7 @@ TUPLE: handle view window ;
 
 C: <handle> handle
 
-TUPLE: cocoa-ui-backend ;
+SINGLETON: cocoa-ui-backend
 
 SYMBOL: stop-after-last-window?
 
@@ -119,6 +119,6 @@ M: cocoa-ui-backend ui
         ] ui-running
     ] with-cocoa ;
 
-T{ cocoa-ui-backend } ui-backend set-global
+cocoa-ui-backend ui-backend set-global
 
 [ running.app? "ui" "listener" ? ] main-vocab-hook set-global

extra/ui/windows/windows.factor

@@ -10,7 +10,7 @@ shuffle opengl ui.render unicode.case ascii math.bitfields
 locals symbols ;
 IN: ui.windows
 
-TUPLE: windows-ui-backend ;
+SINGLETON: windows-ui-backend
 
 : crlf>lf CHAR: \r swap remove ;
 : lf>crlf [ [ dup CHAR: \n = [ CHAR: \r , ] when , ] each ] "" make ;
@@ -496,6 +496,6 @@ M: windows-ui-backend ui
         ] [ cleanup-win32-ui ] [ ] cleanup
     ] ui-running ;
 
-T{ windows-ui-backend } ui-backend set-global
+windows-ui-backend ui-backend set-global
 
 [ "ui" ] main-vocab-hook set-global

extra/ui/x11/x11.factor

@@ -8,7 +8,7 @@ io.encodings.utf8 combinators debugger system command-line
 ui.render math.vectors classes.tuple opengl.gl threads ;
 IN: ui.x11
 
-TUPLE: x11-ui-backend ;
+SINGLETON: x11-ui-backend
 
 : XA_NET_WM_NAME "_NET_WM_NAME" x-atom ;
 
@@ -259,7 +259,7 @@ M: x11-ui-backend ui ( -- )
         ] with-x
     ] ui-running ;
 
-T{ x11-ui-backend } ui-backend set-global
+x11-ui-backend ui-backend set-global
 
 [ "DISPLAY" os-env "ui" "listener" ? ]
 main-vocab-hook set-global