Composable software systems have been proved to support the adaptation to new requirements thanks to their flexibility. A typical method of composable software development is to select and combine a number of patterns that ad-dress the expected quality requirements. Therefore, pattern composition has become a crucial aspect during software design. One of the shortcomings of existing work about pattern composition is the vaporization of composition in-formation which leads to the problem of traceability and reconstructability of patterns. In this paper we propose to give first-class status to pattern merg-ing operators to facilitate the preservation of composition information. The approach is tool-supported and an empirical study has also been conducted to highlight its effectiveness. By applying the approach on the composition of a set of formalized architectural patterns, including their variants, we have shown that composed patterns have become traceable and reconstructable.