September 2017 Update

Task/Power-set/Ada/power-set-1.ada

@@ -1,10 +0,0 @@
-package Power_Set is
-
-   type Set is array  (Positive range <>) of Positive;
-   Empty_Set: Set(1 .. 0);
-
-   generic
-      with procedure Visit(S: Set);
-   procedure All_Subsets(S: Set); -- calles Visit once for each subset of S
-
-end Power_Set;

Task/Power-set/Ada/power-set-2.ada

@@ -1,20 +0,0 @@
-package body Power_Set is
-
-   procedure All_Subsets(S: Set) is
-
-      procedure Visit_Sets(Unmarked: Set; Marked: Set) is
-	 Tail: Set      := Unmarked(Unmarked'First+1 .. Unmarked'Last);
-      begin
-	 if Unmarked = Empty_Set then
-	    Visit(Marked);
-	 else
-	    Visit_Sets(Tail, Marked & Unmarked(Unmarked'First));
-	    Visit_Sets(Tail, Marked);
-	 end if;
-      end Visit_Sets;
-
-   begin
-      Visit_Sets(S, Empty_Set);
-   end All_Subsets;
-
-end Power_Set;

Task/Power-set/Ada/power-set-3.ada

@@ -1,28 +0,0 @@
-with Ada.Text_IO, Ada.Command_Line, Power_Set;
-
-procedure Print_Power_Set is
-
-   procedure Print_Set(Items: Power_Set.Set) is
-      First: Boolean := True;
-   begin
-      Ada.Text_IO.Put("{ ");
-      for Item of Items loop
-	 if First then
-	    First := False; -- no comma needed
-	 else
-	    Ada.Text_IO.Put(", "); -- comma, to separate the items
-	 end if;
-	 Ada.Text_IO.Put(Ada.Command_Line.Argument(Item));
-      end loop;
-      Ada.Text_IO.Put_Line(" }");
-   end Print_Set;
-
-   procedure Print_All_Subsets is new Power_Set.All_Subsets(Print_Set);
-
-   Set: Power_Set.Set(1 .. Ada.Command_Line.Argument_Count);
-begin
-   for I in Set'Range loop -- initialize set
-      Set(I) := I;
-   end loop;
-   Print_All_Subsets(Set); -- do the work
-end;

Task/Power-set/Ada/power-set.ada

@@ -0,0 +1,28 @@
+with Ada.Text_IO, Ada.Command_Line;
+use Ada.Text_IO, Ada.Command_Line;
+
+procedure powerset is
+  procedure print_subset (set : natural) is
+-- each i'th binary digit of "set" indicates if the i'th integer belongs to "set" or not.
+    k : natural := set;
+    first : boolean := true;
+  begin
+    Put ("{");
+    for i in 1..Argument_Count loop
+      if k mod 2 = 1 then
+        if first then
+          first := false;
+        else
+          Put (",");
+        end if;
+        Put (Argument (i));
+      end if;
+      k := k / 2; -- we go to the next bit of "set"
+    end loop;
+    Put_Line("}");
+  end print_subset;
+begin
+  for i in 0..2**Argument_Count-1 loop
+      print_subset (i);
+  end loop;
+end powerset;