Metamorphic Domain-Specific Languages A Journey Into the Shapes of a Language

External or internal domain-specific languages (DSLs) or (fluent) APIs? Whoever you are – a developer or a user of a DSL – you usually have to choose your side; you should not! What about metamorphic DSLs that change their shape according to your needs? We report on our 4-years journey of providing the "right " support (in the domain of feature modeling), leading us to develop an external DSL, different shapes of an internal API, and maintain all these lan-guages. A key insight is that there is no one-size-fits-all solution or no clear superiority of a solution compared to another. On the contrary, we found that it does make sense to continue the maintenance of an external and internal DSL. The vision that we foresee for the future of software languages is their ability to be self-adaptable to the most appropriate shape (includ-ing the corresponding integrated development environment) accord-ing to a particular usage or task. We call metamorphic DSL such a language, able to change from one shape to another shape