//
// Helper function to extract an expression term from a token stream.
//
// Returns true if a term was found, and passes out the index of the
// next token to examine. No tokens should be popped if this helper
// returns false.
//
// Note that in cases where a terminating token is present, such as
// a closing parenthesis or a comma, this will return false; however
// this does not indicate a syntax error.
//
private static bool ParseExpressionTerm(ParseSession parser, bool atstart, int starttoken, out int consumedtokens, out bool matchedstatement)
{
matchedstatement = false;
int totaltokens = starttoken;
consumedtokens = totaltokens;
if (parser.PeekToken(totaltokens) == null)
{
return(false);
}
if (parser.CheckToken(totaltokens, ")"))
{
return(false);
}
if (parser.CheckToken(totaltokens, ","))
{
return(false);
}
if (parser.CheckToken(totaltokens, "("))
{
++totaltokens;
if (Parse(parser, totaltokens, out totaltokens) != null)
{
++totaltokens;
consumedtokens = totaltokens;
return(true);
}
return(false);
}
if (parser.CheckToken(totaltokens, "!"))
{
++totaltokens;
var ret = ParseExpressionTerm(parser, atstart, totaltokens, out totaltokens, out matchedstatement);
if (matchedstatement && parser.CheckToken(totaltokens, ")"))
{
++totaltokens;
}
consumedtokens = totaltokens;
return(ret);
}
// The following check is a tiny optimization. Instead of trying to parse
// a statement first and then eventually giving up, we first try checking
// for common literals. This makes code with literals parse a fractional,
// almost insignificant amount faster. It's actually a relic from the way
// the compiler implements this logic. Maybe it makes sense to remove it,
// and aim for simplicity over ideal efficiency. Profiling data is so far
// insufficient to decide for sure, so this stays in the interim.
if (parser.CheckToken(totaltokens, "false") || parser.CheckToken(totaltokens, "true") || parser.CheckToken(totaltokens, "0") || parser.CheckToken(totaltokens, "0.0"))
{
++totaltokens;
}
else if (parser.ParsePreopStatement(totaltokens, out totaltokens))
{
consumedtokens = totaltokens;
return(true);
}
else if (parser.ParseStatement(totaltokens, out totaltokens))
{
matchedstatement = true;
consumedtokens = totaltokens;
return(true);
}
else
{
++totaltokens;
}
consumedtokens = totaltokens;
return(true);
}