private static RTree ParseSingleSubtree(RevgexStringReader inp, GroupSet groups)
{
var buffer = "";
while (true)
{
switch (inp.Peek())
{
case -1:
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: REmpty.Instance);
case '(':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseAnyGroup(inp, groups));
case ')':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: throw Error(inp, "Unexpected right parenthesis."));
case '*':
case '+':
case '{':
case '?':
if (buffer.Length > 0)
{
if (buffer.Length == 1)
{
return(new RFixedString(buffer, LookupQuantifier(inp)));
}
inp.UnreadEscaped();
return(new RFixedString(buffer.Substring(0, buffer.Length - 1), LookupQuantifier(inp)));
}
throw Error(inp, $"Unexpected character {inp.Peek()}.");
case '\\':
if (TryParseSimpleEscapeSequence(inp, out var ch))
{
buffer += ch;
continue;
}
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseEscapeSequence(inp, groups));
case '$':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseValueReference(inp, groups));
case '.':
if (buffer.Length > 0)
{
return(new RFixedString(buffer, QuantifierOne.Instance));
}
else
{
inp.Read();
return(RChar.Dot(LookupQuantifier(inp)));
}
case '[':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseCharSet(inp));
case '|':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: REmpty.Instance);
default:
buffer += inp.Read();
continue;
}
}
}