Beispiel #1
0
  /**
   * Alternates NFAs r and s
   *
   * <p>As a side effect, changes all the NFANodes inside each NFA r and s to be no longer accepting
   * and instead have epsilon transitions out to a resulting accept state
   *
   * @param r
   * @param s
   * @return An NFA that matches either r or s
   */
  public static NFA alternation(NFA r, NFA s) {
    NFA nfa = new NFA();

    nfa.nodes.addAll(r.nodes);
    nfa.nodes.addAll(s.nodes);

    // create start node and set eps trans to beginning of a and b
    NFANode start = new NFANode();
    nfa.nodes.add(start);
    nfa.initial = start;
    start.addEpsilonTransition(r.initial);
    start.addEpsilonTransition(s.initial);

    // set end node as accepting
    NFANode end = new NFANode();
    nfa.nodes.add(end);
    end.setAccepting(true);

    // set all accepting nodes in A and B as non-accepting and
    // add eps-trans out to end node
    for (NFANode n : r.nodes) {
      if (n.isAccepting()) {
        n.addEpsilonTransition(end);
        n.setAccepting(false);
      }
    }
    for (NFANode n : s.nodes) {
      if (n.isAccepting()) {
        n.addEpsilonTransition(end);
        n.setAccepting(false);
      }
    }

    return nfa;
  }
Beispiel #2
0
  /**
   * An NFA that matches the given character or epsilon if c is null
   *
   * @param c If null, creates an NFA that matches an epsilon transition (always match)
   */
  public static NFA basicMatch(Character c) {
    NFA nfa = new NFA();

    NFANode n1 = new NFANode();
    NFANode n2 = new NFANode();

    n1.addTransition(c, n2);
    n2.setAccepting(true);

    nfa.initial = n1;

    nfa.nodes.add(n1);
    nfa.nodes.add(n2);

    return nfa;
  }
Beispiel #3
0
  /**
   * Concatenates NFAs r and s
   *
   * <p>As a side effect, this causes all the NFANodes that were accepting before to become
   * non-accepting and instead have epsilon transitions to the start state of s.
   *
   * @param r
   * @param s
   * @return A new NFA that is the concatenation of those two
   */
  public static NFA concatenation(NFA r, NFA s) {
    NFA nfa = new NFA();

    nfa.nodes.addAll(r.nodes);
    nfa.nodes.addAll(s.nodes);

    // add eps-trans from a's accept to b's initial and remove a's accept flags
    for (NFANode node : r.nodes) {
      if (node.isAccepting()) {
        node.addEpsilonTransition(s.initial);
        node.setAccepting(false);
      }
    }

    nfa.initial = r.initial;

    return nfa;
  }