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 COED is a screen editor for the BBC Micro written in 6502 assembler.  

 Author:   Graham Toal
 Family:   LineEditorFamily EdinburghFamily
 Platform: BBC Micro
 License:  Commercial

It uses the "buffer gap" technique, and rolls out blocks from either end of the file to two temporary disk files when editing documents larger than the BBC Micro's relatively small memory. Source is available and will be online shortly. The internals of COED are derived from the internals of ECCE, a line editor. This editor was written as a demonstration for Acorn staff, whose only existing text editor at that time used a single contiguous text area for its "data structure" (making inserts painfully slow, as you could imagine). This editor was responsible for exploding "editor wars" at Acorn, where Sophie (at the time, Roger) Wilson, Ben Bridgwater, Keith Rautenbach, Jon Thackray and Graham Toal all worked on competing text editors. Competition was good for business and Acorn subsequently turned out several text editors that were far better than their earlier efforts.

Keith Rautenbach's editor was a LISP-based editor in the style of EMACS but not quite so bloated, and written in Modula-II. The source was rediscovered recently and will be online soon. Ben Bridgwater's editor was the program editor for Acorn's Pascal, and a floppy which may contain this code has been located; once the disk is recovered it will be put online.

An early source of COED (V0.1) has been located and is online for now at

The editor does not fold long lines; rather, it allows for sideways scroll. Also it assumes a model of one byte = one display character, when handling vertical movement, using an inverse video symbol for unprintable characters.

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Last edited May 19, 2009 8:52 am (diff)