Abstract
Best practices in programming typically imply coding using classes and interfaces that are not (fully) defined yet. However, integrated development environments (IDEs) do not support such incremental programming seamlessly. Instead, they get in the way by reporting ineffective error messages. Ignoring these messages altogether prevents the programmer from getting useful feedback regarding actual inconsistencies and type errors. But attending to these error messages repeatedly breaks the programming workflow. In order to smoothly support incremental programming, we propose to extend IDEs with support of undefined entities, called Ghosts. Ghosts are implicitly reified in the IDE through their usages. Programmers can explicitly identify ghosts, get appropriate type feedback, interact with them, and bust them when ready, yielding actual code.