/////////////////////////////////////////////////////////////////
//
// NFA building functions
//
// Using Thompson Construction, build NFAs from basic inputs or
// compositions of other NFAs.
//
/// <summary>
/// Builds a basic, single input NFA
/// </summary>
/// <param name="in"></param>
/// <returns></returns>
public static NFA BuildNFABasic(input @in)
{
NFA basic = new NFA(2, 0, 1);
basic.AddTrans(0, 1, @in);
return(basic);
}
/// <summary>
/// Builds a star (kleene closure) of nfa (nfa*)
/// How this is done: First will come the new initial state, then NFA, then the
/// new final state
/// </summary>
/// <param name="nfa"></param>
/// <returns></returns>
public static NFA BuildNFAStar(NFA nfa)
{
// Makes room for the new initial state
nfa.ShiftStates(1);
// Makes room for the new final state
nfa.AppendEmptyState();
// Adds new transitions
nfa.AddTrans(nfa.final, nfa.initial, (char)Constants.Epsilon);
nfa.AddTrans(0, nfa.initial, (char)Constants.Epsilon);
nfa.AddTrans(nfa.final, nfa.size - 1, (char)Constants.Epsilon);
nfa.AddTrans(0, nfa.size - 1, (char)Constants.Epsilon);
nfa.initial = 0;
nfa.final = nfa.size - 1;
return(nfa);
}
/// <summary>
/// Builds an alternation of nfa1 and nfa2 (nfa1|nfa2)
/// </summary>
/// <param name="nfa1"></param>
/// <param name="nfa2"></param>
/// <returns></returns>
public static NFA BuildNFAAlter(NFA nfa1, NFA nfa2)
{
// How this is done: the new nfa must contain all the states in
// nfa1 and nfa2, plus a new initial and final states.
// First will come the new initial state, then nfa1's states, then
// nfa2's states, then the new final state
// make room for the new initial state
nfa1.ShiftStates(1);
// make room for nfa1
nfa2.ShiftStates(nfa1.size);
// create a new nfa and initialize it with (the shifted) nfa2
NFA newNFA = new NFA(nfa2);
// nfa1's states take their places in new_nfa
newNFA.FillStates(nfa1);
// Set new initial state and the transitions from it
newNFA.AddTrans(0, nfa1.initial, (char)Constants.Epsilon);
newNFA.AddTrans(0, nfa2.initial, (char)Constants.Epsilon);
newNFA.initial = 0;
// Make up space for the new final state
newNFA.AppendEmptyState();
// Set new final state
newNFA.final = newNFA.size - 1;
newNFA.AddTrans(nfa1.final, newNFA.final, (char)Constants.Epsilon);
newNFA.AddTrans(nfa2.final, newNFA.final, (char)Constants.Epsilon);
return(newNFA);
}
