diff --git a/collects/mred/edit.ss b/collects/mred/edit.ss
index e0510453..f05e9180 100644
--- a/collects/mred/edit.ss
+++ b/collects/mred/edit.ss
@@ -1,9 +1,14 @@
 (define mred:edit@
-  (unit/s mred:edit^
-    (import [mred:debug mred:debug^] [mred:finder mred:finder^]
-	    [mred:path-utils mred:path-utils^] [mred:mode mred:mode^]
-	    [mred:scheme-paren mred:scheme-paren^] [mred:keymap mred:keymap^]
-	    [mzlib:function mzlib:function^])
+  (unit/sig mred:edit^
+    (import ([unit mred:debug : mred:debug^]
+	     [unit mred:finder : mred:finder^]
+	     [unit mred:path-utils : mred:path-utils^]
+	     [unit mred:mode : mred:mode^]
+	     [unit mred:scheme-paren : mred:scheme-paren^]
+	     [unit mred:keymap : mred:keymap^]
+	     [unit mzlib:function : mzlib:function^]))
+	    
+    (mred:debug:printf 'invoke "mred:edit@")
 
     (define-struct range (start end b/w-bitmap color))
     (define-struct rectangle (left top width height b/w-bitmap color))
diff --git a/collects/mred/exit.ss b/collects/mred/exit.ss
index 04b1d5cd..8e611e28 100644
--- a/collects/mred/exit.ss
+++ b/collects/mred/exit.ss
@@ -1,8 +1,10 @@
 (define mred:exit@
-  (unit/s mred:exit^
-    (import [mred:debug mred:debug^])
+  (unit/sig mred:exit^
+    (import ([unit mred:debug : mred:debug^]))
     (rename (-exit exit))
 
+    (mred:debug:printf 'invoke "mred:exit@")
+
     (define exit-callbacks '())
     
     (define insert-exit-callback
diff --git a/collects/mred/finder.ss b/collects/mred/finder.ss
index 23ddbc47..b836e10e 100644
--- a/collects/mred/finder.ss
+++ b/collects/mred/finder.ss
@@ -1,7 +1,11 @@
 (define mred:finder@
-  (unit/s mred:finder^
-    (import [mred:debug mred:debug^] [mzlib:string mzlib:string^]
-	    [mzlib:function mzlib:function^] [mzlib:file mzlib:file^])
+  (unit/sig mred:finder^
+    (import ([unit mred:debug : mred:debug^]
+	     [unit mzlib:string : mzlib:string^]
+	     [unit mzlib:function : mzlib:function^]
+	     [unit mzlib:file : mzlib:file^]))
+	    
+    (mred:debug:printf 'invoke "mred:finder@")
 
     (define filter-match?
       (lambda (filter name msg)
diff --git a/collects/mred/keys.ss b/collects/mred/keys.ss
index 487890b5..bfed8ef7 100644
--- a/collects/mred/keys.ss
+++ b/collects/mred/keys.ss
@@ -1,10 +1,12 @@
 (define mred:keymap@
-  (unit/s mred:keymap^
-    (import [mred:debug mred:debug^] [mred:finder mred:finder^]
-	    [mred:handler mred:handler^] [mred:find-string mred:find-string^]
-	    [mred:scheme-paren mred:scheme-paren^])
-
-    (mred:debug:printf "mred:keymap@")
+  (unit/sig mred:keymap^
+    (import ([unit mred:debug : mred:debug^]
+	     [unit mred:finder : mred:finder^]
+	     [unit mred:handler : mred:handler^]
+	     [unit mred:find-string : mred:find-string^]
+	     [unit mred:scheme-paren : mred:scheme-paren^]))
+	    
+    (mred:debug:printf 'invoke "mred:keymap@")
 
     ; This is a list of keys that are typed with the SHIFT key, but
     ;  are not normally thought of as shifted. It will have to be
diff --git a/collects/mred/prefs.ss b/collects/mred/prefs.ss
index 1a4d32b0..157a4adb 100644
--- a/collects/mred/prefs.ss
+++ b/collects/mred/prefs.ss
@@ -6,10 +6,12 @@
 ;; to see if it needs to be unmarshalled.
 
 (define mred:preferences@
-  (unit/s mred:preferences^
-    (import [mred:debug mred:debug^]
-	    [mred:exn mred:exn^]
-	    [mzlib:function mzlib:function^])
+  (unit/sig mred:preferences^
+    (import ([unit mred:debug : mred:debug^]
+	     [unit mred:exn : mred:exn^]
+	     [unit mzlib:function : mzlib:function^]))
+
+    (mred:debug:printf 'invoke "mred:preferences@")
     
     (define preferences-filename
       (case wx:platform