Re: Stumped without mutation...

[jap]

Perhaps it time to recall a system called Flex, that was developed at
the (then) Royal Signals and Radar Establishment at Malvern in the
late 1970s.  The hardware was custom and microprogrammable, with an
operating system, (modular) compiler, editor, garbage collector,
filing system etc. all written in Algol-68.  I think there was also a
re-implementation on the Perq.  No doubt others can supply more precise
details...

--Julian