I've checked these all against the Darcs history using a script
(check-copyright, in my misccode collection). Anything Neil or I did as
part of our PhDs is copyright University of Kent; more recent work
belongs to us, as appropriate.
Previously it was a tuple, which meant it couldn't have sensible
custom instances. Token and TokenType now have Show instances, so we
get more useful output when parsing fails.
The order of initial passes is now:
lex -> preprocess -> structure -> expand-include -> parse
which means that #IFing out structurally-invalid code (like inline VALOF) now
works. This also cleans up the preprocessor code a bit.
