private IAutomaton Factor()
{
if (MayConsume('('))
{
var result = Exec();
Consumes(')');
return(result);
}
else if (MayConsume('['))
{
var negate = MayConsume('^');
var chars = CharSet.Empty;
while (!MayConsume(']'))
{
var set = CharRange();
chars = chars.Union(set);
}
if (negate)
{
chars = chars.Negate();
}
return(ConstructionKit.Consume(chars));
}
else
{
var ch = CharRange();
return(ConstructionKit.Consume(ch));
}
}
private IAutomaton PrimaryExpression()
{
var operand = Factor();
switch (Lookahead)
{
case '*': index++; return(ConstructionKit.Repeat(operand));
case '+': index++; return(ConstructionKit.Repeat(operand, 1));
case '?': index++; return(ConstructionKit.Repeat(operand, 0, 1));
case '{':
index++;
var min = Number();
if (MayConsume(','))
{
var max = Number();
Consumes('}');
return(ConstructionKit.Repeat(operand, min, max));
}
else
{
Consumes('}');
return(ConstructionKit.Repeat(operand, min, min));
}
}
return(operand);
}
public void StepConcatenation()
{
var A = ConstructionKit.Consume(new CharSet('a'));
var B = ConstructionKit.Consume(new CharSet('b'));
var automaton = ConstructionKit.Concat(new[] { A, B });
automaton.Accepts("ab");
automaton.Rejects("ba");
}
public void StepCharacter()
{
var automaton = ConstructionKit.Consume(new CharSet('a', 'b', 'c'));
automaton.Accepts("a");
automaton.Accepts("b");
automaton.Accepts("c");
automaton.Rejects("d");
}
public void StepRepetition()
{
var A = ConstructionKit.Consume(new CharSet('a'));
var automaton = ConstructionKit.Repeat(A);
automaton.Accepts("");
automaton.Accepts("a");
automaton.Accepts("aa");
automaton.Accepts("aaa");
automaton.Rejects("b");
}
public void StepAlternation()
{
var A = ConstructionKit.Consume(new CharSet('a'));
var B = ConstructionKit.Consume(new CharSet('b'));
var AA = ConstructionKit.Concat(new[] { A, A });
var automaton = ConstructionKit.Alternate(new[] { AA, B });
automaton.Accepts("b");
automaton.Accepts("aa");
automaton.Rejects("bb");
automaton.Rejects("a");
}
private IAutomaton ConcatExpression()
{
var lhs = PrimaryExpression();
while (Lookahead != '|' && Lookahead != Eos && Lookahead != ')')
{
var rhs = PrimaryExpression();
lhs = ConstructionKit.Concat(new[]
{
lhs, rhs
});
}
return(lhs);
}
public IAutomaton Exec()
{
var lhs = ConcatExpression();
while (Lookahead == '|')
{
index++;
var rhs = ConcatExpression();
lhs = ConstructionKit.Alternate(new[]
{
lhs, rhs
});
}
return(lhs);
}
public void StepDeterminize()
{
var A = ConstructionKit.Consume(new CharSet('a'));
var B = ConstructionKit.Consume(new CharSet('b'));
var AA = ConstructionKit.Concat(new[] { A, A });
var AAorB = ConstructionKit.Alternate(new[] { AA, B });
var automaton = ConstructionKit.Repeat(AAorB)
.Determinize();
automaton.Accepts("");
automaton.Accepts("aa");
automaton.Accepts("aa");
automaton.Accepts("aaaa");
automaton.Accepts("baab");
automaton.Accepts("baabaabb");
automaton.Rejects("a");
automaton.Rejects("aaa");
}
