ASCII-based or tree-based editing: an intricate choice

Most users are used to edit source code using a conventional editor like Emacs, while presenting the source code in ASCII format. Since all TeXmacs documents are stored as trees, an interesting but complicated question is which format is most suitable for editing such documents. One option is to represent the tree using an ASCII-based format, such as XML, Scheme, or the native format for storing files on a disk. The other option is to edit the trees as such, making no fundamental distinction between source code and normal documents.

In TeXmacs we have chosen to implement the second option. More precisely, any document can be edited in “source mode”, which is merely a mode for rendering the document in a way which makes its tree structure particularly apparent. It may be instructive to take an arbitrary document of yours and to take a look at it in “source mode” by enabling Document→View→Edit source tree.

The choice between ASCII-based editing and tree-based editing is non-trivial, because TeXmacs style files and packages have a double nature: they may be seen as programs which specify how to render macros, but these programs naturally contain ordinary content. There are several reasons why users often prefer to edit source code in an ASCII-based format:

1. It is easy to manually format the code so as to make it more readable.
2. In particular, it is easy to add comments.
3. Standard editors like Emacs provide tools for automatic highlighting, indentation, etc.
4. One is not constraint by any “structure” during the editing phase.

Our approach is to reproduce as much of the above advantages in a structured document environment. Although point ? will obviously be hard to meet when following this approach, we believe that the first three advantages might actually become greater in a structured environment. However, this requires a more profound understanding of how users format and edit source code.

For instance, consider a piece of manually formatted code like

if (cond) hop   = 2;
else      holala= 3;

Clearly, the user had a particular formatting policy when writing this code. However, this policy does not appear in the document: manual intervention will be necessary if the variable cond is renamed c, or if the variable holala is renamed hola.

At the moment, TeXmacs provides no tools for dealing with the above example in an automatic way, but a few tools are already provided. For instance, the user is given a great amount of control on how to indent source code and reasonable defaults are provided as a function of the structure. We also provide high level environments for comments and structured highlighting. Further tools will be developed later and we are open for any suggestions from our users.