We are currently implementing a system to help experienced programmers during the development, implementation and debugging of their programs. This system, built on top of a screen oriented structural editor, offers possibilities to attach descriptors to every portion of the program and to maintain - simultaneously - different versions of the program being written, including tentative hypothetical versions. It comprises a mecanism to maintain minimal consistency between modified parts of code, the non-modified parts of code and the attached descriptors, as well as an evaluation module functioning in different modes: normal evaluation, symbolic evaluation and checking evaluation . The standard programming aids, such as indexors, pretty printers, trace packages, undo- and history-facilities are generalized to handle the descriptors and unfinished programs as well