private NFAState ParseExpr(NFAState start)
{
NFAState end = new NFAState();
do
{
if (PeekChar(0) == '|')
{
ReadChar('|');
}
var subStart = new NFAState();
var subEnd = ParseTerm(subStart);
if (subStart.Incoming.Length == 0)
{
subStart.MergeInto(start);
}
else
{
start.AddOut(new NFAEpsilonTransition(subStart));
}
if (subEnd.Outgoing.Length == 0 ||
(!end.HasTransitions() && PeekChar(0) != '|'))
{
subEnd.MergeInto(end);
}
else
{
subEnd.AddOut(new NFAEpsilonTransition(end));
}
} while (PeekChar(0) == '|');
return(end);
}
private NFAState ParseFact(NFAState start)
{
NFAState placeholder = new NFAState();
var end = ParseAtom(placeholder);
switch (PeekChar(0))
{
case '?':
case '*':
case '+':
case '{':
end = ParseAtomModifier(placeholder, end);
break;
}
if (placeholder.Incoming.Length > 0 && start.Outgoing.Length > 0)
{
start.AddOut(new NFAEpsilonTransition(placeholder));
return(end);
}
else
{
placeholder.MergeInto(start);
return((end == placeholder) ? start : end);
}
}
private NFAState ParseAtomModifier(NFAState start, NFAState end)
{
int min = 0;
int max = -1;
int firstPos = _pos;
// Read min and max
switch (ReadChar())
{
case '?':
min = 0;
max = 1;
break;
case '*':
min = 0;
max = -1;
break;
case '+':
min = 1;
max = -1;
break;
case '{':
min = ReadNumber();
max = min;
if (PeekChar(0) == ',')
{
ReadChar(',');
max = -1;
if (PeekChar(0) != '}')
{
max = ReadNumber();
}
}
ReadChar('}');
if (max == 0 || (max > 0 && min > max))
{
throw new RegExpException(
RegExpException.ErrorType.INVALID_REPEAT_COUNT,
firstPos,
_pattern);
}
break;
default:
throw new RegExpException(
RegExpException.ErrorType.UNEXPECTED_CHARACTER,
_pos - 1,
_pattern);
}
// Read possessive or reluctant modifiers
if (PeekChar(0) == '?')
{
throw new RegExpException(
RegExpException.ErrorType.UNSUPPORTED_SPECIAL_CHARACTER,
_pos,
_pattern);
}
else if (PeekChar(0) == '+')
{
throw new RegExpException(
RegExpException.ErrorType.UNSUPPORTED_SPECIAL_CHARACTER,
_pos,
_pattern);
}
// Handle supported repeaters
if (min == 0 && max == 1)
{
return(start.AddOut(new NFAEpsilonTransition(end)));
}
else if (min == 0 && max == -1)
{
if (end.Outgoing.Length == 0)
{
end.MergeInto(start);
}
else
{
end.AddOut(new NFAEpsilonTransition(start));
}
return(start);
}
else if (min == 1 && max == -1)
{
if (start.Outgoing.Length == 1 &&
end.Outgoing.Length == 0 &&
end.Incoming.Length == 1 &&
start.Outgoing[0] == end.Incoming[0])
{
end.AddOut(start.Outgoing[0].Copy(end));
}
else
{
end.AddOut(new NFAEpsilonTransition(start));
}
return(end);
}
else
{
throw new RegExpException(
RegExpException.ErrorType.INVALID_REPEAT_COUNT,
firstPos,
_pattern);
}
}