Software modernization powered by dynamic language product lines

Legacy software poses a critical challenge for organizations due to the costs of maintaining and modernizing outdated systems, as well as the scarcity of experts in aging programming languages. The issue extends beyond commercial applications, affecting public administration, as exemplified by the urgent need for COBOL programmers during the COVID-19 pandemic. In response, this work introduces a modernization approach based on dynamic language product lines, a subset of dynamic software product lines. This approach leverages open language implementations and dynamically generated micro-languages for the incremental migration of legacy systems to modern technologies. The language can be reconfigured at runtime to adapt to the execution of either legacy or modern code, and to generate a compatibility layer between the data types handled by the two languages. Through this process, the costs of modernizing legacy systems can be spread across several iterations, as developers can replace legacy code incrementally, with legacy and modern code coexisting until a complete refactoring is possible. By moving the overhead of making legacy and modern features work together in a hybrid system from the system implementation to the language implementation, the quality of the system itself does not degrade due to the introduction of glue code. To demonstrate the practical applicability of this approach, we present a case study on a COBOL system migration to Java. Using the Neverlang language workbench to create modular and reconfigurable language implementations, both the COBOL interpreter and the application evolve to spread the development effort across several iterations. Through this study, this work presents a viable solution for organizations dealing with the complexity of modernizing legacy software to contemporary technologies. The contributions of this work are (i) a language-oriented, incremental refactoring process for legacy systems, (ii) a concrete application of open language implementations, and (iii) a general template for the implementation of interoperability between languages in hybrid systems.