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Histogram : Map;  -- String key, Integer element
...
procedure Add (Word : in String) is
  procedure Increment_Count
    (Key : in String; Count : in out Integer) is
  begin
     Count := Count + 1;
  end;
  C : constant Cursor := Histogram.Find (Word);
begin
  if Has_Element (C) then  -- found
     Update_Element (C, Increment_Count’Process);
  else     
     Histogram.Insert (Word, 1);
  end if;
end Add;