def _nt_optional_suffix
start_index = index
if node_cache[:optional_suffix].has_key?(index)
cached = node_cache[:optional_suffix][index]
if cached
node_cache[:optional_suffix][index] = cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
@index = cached.interval.end
end
return cached
end
if (match_len = has_terminal?('?', false, index))
r0 = instantiate_node(Optional,input, index...(index + match_len))
@index += match_len
else
terminal_parse_failure('\'?\'')
r0 = nil
end
node_cache[:optional_suffix][start_index] = r0
r0
end