added Table.map_default

--- a/src/Pure/General/table.ML	Tue Jul 18 02:22:38 2006 +0200
+++ b/src/Pure/General/table.ML	Tue Jul 18 08:48:11 2006 +0200
@@ -39,6 +39,7 @@
   val update_new: (key * 'a) -> 'a table -> 'a table                   (*exception DUP*)
   val default: key * 'a -> 'a table -> 'a table
   val map_entry: key -> ('a -> 'a) -> 'a table -> 'a table
+  val map_default: (key * 'a) -> ('a -> 'a) -> 'a table -> 'a table
   val make: (key * 'a) list -> 'a table                                (*exception DUPS*)
   val extend: 'a table * (key * 'a) list -> 'a table                   (*exception DUPS*)
   val join: (key -> 'a * 'a -> 'a) (*exception DUP/SAME*) ->
@@ -246,6 +247,7 @@
 fun update_new (key, x) tab = modify key (fn NONE => x | SOME _ => raise DUP key) tab;
 fun default (key, x) tab = modify key (fn NONE => x | SOME _ => raise SAME) tab;
 fun map_entry key f = modify key (fn NONE => raise SAME | SOME x => f x);
+fun map_default (key, x) f = modify key (fn NONE => f x | SOME x => f x);
 
 
 (* delete *)