private Tuple <NfaState, NfaState> buildNfa(Exp ast)
{
NfaState start = null;
NfaState terminal = null;
if (ast.Type != Exp.ExpType.Concat)
{
start = CreateState();
terminal = CreateState();
}
switch (ast.Type)
{
case Exp.ExpType.Token:
{
AddEdge(start, terminal, ast.C);
break;
}
case Exp.ExpType.Concat:
{
var nfa1 = buildNfa(ast.E1);
var nfa2 = buildNfa(ast.E2);
start = nfa1.Item1;
terminal = nfa2.Item2;
AddEdge(nfa1.Item2, nfa2.Item1, EPSILON);
break;
}
case Exp.ExpType.Alter:
{
var nfa1 = buildNfa(ast.E1);
var nfa2 = buildNfa(ast.E2);
AddEdge(start, nfa1.Item1, EPSILON);
AddEdge(start, nfa2.Item1, EPSILON);
AddEdge(nfa1.Item2, terminal, EPSILON);
AddEdge(nfa2.Item2, terminal, EPSILON);
break;
}
case Exp.ExpType.Kleene:
{
var nfa = buildNfa(ast.E1);
AddEdge(start, terminal, EPSILON);
AddEdge(start, nfa.Item1, EPSILON);
AddEdge(nfa.Item2, nfa.Item1, EPSILON);
AddEdge(nfa.Item2, terminal, EPSILON);
break;
}
}
return(new Tuple <NfaState, NfaState> (start, terminal));
}