private Swap ParseSwap()
{
var tx = _stream.Fixate();
var arg0 = ParsePrimary();
if (arg0 == null)
{
return(null);
}
var t = NextToken();
if (!t.IsOperator(Operator.AssignSwap))
{
_stream.Rollback(tx); // Undo operator and 'primary' read
return(null);
}
var node = new Swap();
node.AddChild(arg0);
var arg1 = ParsePrimary();
if (arg1 == null)
{
throw SyntaxError.Make(SyntaxErrorMessages.PRIMARY_EXPECTED, t);
}
node.AddChild(arg1);
t = NextToken();
AssertDelimiter(Delimiter.Semicolon, t);
return(node);
}