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  my $class = ref($type) || $type;
  my $parameters = shift;
  my $self = {};
  $self->{default_first_search_step} = \&first_search_step;
  $self->{default_search_type} = 'dfs';
  $self->{default_search_step} = \&search_step;
  bless $self, $class;
  return $self;
}


1;

__END__

=head1 NAME

Algorithm::Search - Module for traversing an object.

=head1 SYNOPSIS

  use Algorithm::Search;
  my $as = new Algorithm::Search();

  $as->search({ # Example parameters here are the default parameters
   search_this => $object_to_search, #no default
   search_type => 'dfs', # dfs, bfs, cost, or rdfs
   max_steps => 20000, # number of moves to look at
   maximum_depth => 0, # longest allowable path length if > 0
   solutions_to_find => 0, # search stops when number reached, 0 finds all
   do_not_repeat_values => 0, # only traverse position with value once
   cost_cannot_increase => 0, # whether or not moves can increase cost
   initial_cost => undef, # for cost based search
   return_search_trace => 0, # does $as->search_trace return array ref of moves
  });
  if (!$as->completed) {
    $as->continue_search({additional_steps => 300});
  }

  if ($as->solution_found) {
    @solutions = $as->solutions;
    @paths_to_solution = $as->paths;
  }

  $steps_taken = $search->steps_taken;


=head1 DESCRIPTION AND DEFINITIONS

A user provided traversable object starts in an initial position.
The traversable
object must have certain methods, such as 'move', described below.
This is passed into the search method via the 'search_this' parameter.

At any position, the object has a list of moves to new positions,
the list may be empty.

A position is a solution if the "is_solution" function returns true.

A traversal does not require that a solution be found or even looked for.
A search is a traversal that looks for a solution.

A path corresponds to a list of valid moves from the initial position.
The path values correspond to the list of values by the positions
the object moves along the path.

A move is valid if the move function returns a value.
The number of steps, is the number of calls to the move function.

A queue based traversal stores positions and paths on a queue, copying
the object before performing each move.

In depth first search (dfs), the next position to search is the
most recently placed on the queue.

In breadth first search (bfs), the next item to search is the least
recently placed on the queue.

In cost based search (cost) , the next item to search is the lowest
cost item on the queued, ties go to the most recently placed on the queue.
Cost based search with all the same costs behaves as depth first search.

A reversible depth first search (rdfs) traversal uses
reverse move to traverse paths with the search object.
A reversible traversal does not use a queue resulting in less memory
usage.  A reversible traversal is more complicated to set up and only
allows depth first search.

=head1 Methods Required in object being searched.

=head2 Common to all Searches

  sub move ($move, $cost)
   #required, return undef if illegal move else return cost

If the parameter cost_cannot_increase is set, any move which
would decrease the cost is disallowed.  The cost is the value
returned from the move method.

The search parameter initial_cost corresponds to where in the
queue the moves from the initial position belong.

  sub value #optional - used to pare down search, a value cannot
   #repeat on a search path, prevents loops in paths

If the parameter do_not_repeat_values is set, a value cannot
repeat any time in the search.  Presumably this would be done to
find a single solution and not be concerned about the paths.

  sub stop_search #optional - after every step, this procedure
   #is passed the current position, the number of steps,
   #and the path to the current position.  If it returns
   #a true value, the search stops.  Useful for tracing the search.

=head2 Depth First, Breadth First, and Cost Queue-Based Searches

  sub next_moves #required, list of moves from given object

  sub copy #required

  sub commit_level #optional - returns number, used to pare down search