contents | what does expander do? >

Expanding NEdit

Steven Haehn and Joor Loohuis

contents

• introduction
• history
• what does expander do?
• getting it to work with NEdit
• personalized expansion
• there's more
• expander in action
• availability

introduction

Expander is a utility that acts as a filter for text editors, and replaces specific short character sequences, or abbreviations, with longer ones. The replacement text may contain newlines, indents, and even the contents of entire files (templates). It can also contain various control features, and markers can be used to control cursor placement in NEdit. It provides a simple mechanism through which rapid prototyping and consistent formatting in NEdit are easily obtained.

history

Expander has been available for some time from the NEdit site, but it has undergone quite some changes over the years. Steve explains:

The idea for the expander facility came from my experiences at Xerox using a programming tool called the Xerox Development Environment (XDE). Inside XDE was a "Definition" mechanism that allowed user's to define abbreviations and have them expanded by the stroke of a special key on the keyboard. It was somewhat primitive in that it's forte was really to take simple typing abbreviations, such as XDE, and expand it to its stored definition of "Xerox Development Environment". The Unix 'vi' and 'emacs' editors also share this similar capability. However, none of these editing environments satisfied my itch. I wanted more than what they could provide.

Eventually, a colleague introduced me to NEdit, and I was off learning how this newly discovered editor worked. I had forgotten about the XDE environment abbreviation expander, until I found the original expander code created for NEdit by Marc Verdiesen. I saw how it was put together and thought to myself that with some tweaking (which eventually became almost a complete rewrite), I could allow individuals to define their own definitions, like the XDE environment did. I was off and running, ...uh, programming. (Since I am not a great typist, I go to great lengths to figure out how to be able to generate good looking, readable code, with minimal effort from my meager typing skills.)

The original code was locked into the 'C' programming language and had to be modified to make additions. To get around this I made the program get all its definitions from data files instead of fixed data in the program. This allows the user to declare their own definitions without having to modify the program. It also gives everyone the freedom to specify how they want their programming constructs to be expanded. For instance, where do the enclosing braces on a programming statement reside; on the same line as the statement introductory clause, or on the next line under the clause? The program allows the user to define these embellishments, not the other way around, with the program dictating how the statement looks. So that was one goal; to bring data definitions out of the program into the hands of the user.

Since I program in many languages, a second goal took shape. This was the goal of language sensitive definitions. I wanted to be able to get an 'if' statement produced in an individual's programming work without having to worry about the explicit syntax. So whether one is programming in perl, Java, 'C', shell scripts, whatever, all that would be needed to do is enter 'if' and expand the definitions according to current language setting. To me, this frees the programmer from worrying about syntax issues and allows them to concentrate on the algorithm being developed.

When I was introduced to NEdit, I was working in a group which had set up some standards on how the code being produced was to look and be documented. This was leading me down the path of file template expansion, which became an expander feature. I not only wanted to expand an abbreviation into the contents of an existing template, I wanted fields in the template to be dynamically filled in. The goal was to allow generic templates to become personalized when expanded by an individual. For instance, the name of the individual applying the expansion and the date the expansion was applied could be now automatically filled in. This is how the dynamic auto-fill field feature came into being. It can be thought of as recursive abbreviation expansion. That is, the expander facility is automatically expanding fields containing abbreviation for which it already has definitions.

contents | what does expander do? >