Active Text for Structuring and Understanding Source Code

2 SUMMARY Programs are not read sequentially like a book but rather selectively like an encyclopedia. Instead of linear text we therefore suggest non-linear active text as a medium for structuring and browsing source code. While common program editors are mainly character based we believe that non-textual information such as pictures, links, folds, and annotations can improve the readability of programs. In this paper we show how a text editor can be extended to include active text elements and give examples for how to apply these facilities to source code. Our approach is different from that of syntax-oriented editors in that our structuring is not based on the syntax of the edited texts. The implementation was done in the Oberon system which offers powerful mechanisms for extending software in an object-oriented way.