package edu.stanford.nlp.parser.common;

import java.io.Serializable;
import java.util.regex.Pattern;



/** 
 * A Constraint represents a restriction on possible parse trees to
 * consider.  It says that a parse cannot be postulated that would
 * contradict having a constituent from position start to end, and
 * that any constituent postulated with this span must match the
 * regular expression given by state.  Note, however, that it does not
 * strictly guarantee that such a constituent exists in a returned
 * parse.
 * <br>
 * The words in constraint bounds are counted starting from 0.
 * Furthermore, the end number is not included in the constraint.
 * For example, a constraint covering the first two words of a
 * sentence has a start of 0 and an end of 2.
 * <br>
 * state must successfully match states used internal to the parser,
 * not just the final states, so the pattern "NP" will not match
 * anything.  Better is "NP.*".  Note that this does run the risk of
 * matching states with the same prefix.  For example, there is SBAR
 * and SBARQ, so "SBAR.*" could have unexpected results.  The states
 * used internal to the parser extend the state name with
 * non-alphanumeric characters, so a fancy expression such as
 * "SBAR|SBAR[^a-zA-Z].*" would match SBAR but not SBARQ constituents.
 */
public class ParserConstraint implements Serializable {
  public final int start;
  public final int end;
  public final Pattern state;
  
  private static final long serialVersionUID = 2;

  //public ParserConstraint() {}

  public ParserConstraint(int start, int end, String pattern) {
    this(start, end, Pattern.compile(pattern));
  }

  public ParserConstraint(int start, int end, Pattern state) {
    this.start = start;
    this.end = end;
    this.state = state;
  }

  @Override
  public String toString() {
    return "ParserConstraint(" + start + "," + end + ":" + state + ")";
  }
}