Let’s start with a quick recap for those of you who are just tuning in (and for those who have been tuned in for a while but are likely very lost):

• In the late 80s, Psion developed their own message-passing Object Oriented C dialect with its own markup language. They did this because Psion be Psion-ing. This is a recurring theme.
• CTRAN.EXE, a 16-bit DOS app, is Psion’s OO preprocessor. It takes class declaration files using this OO markup language (called “category files” by no one but Psion – see the previous point) and translates them into C and Turbo Assembler code.
• The C generator in CTRAN.EXE is rudimentary but very reliable.
• The TASM generator is, shall we say, less optimal. There are bugs. Sometimes it crashes. I’m convinced no one actually used it.

Here’s an example category file. If you’ve written parsers before, you’ll enjoy trying to wrap your head around this format!