> This is perfectly right, and as always with mutable values, you cannot
> implement a feature without adding some safeguard conditions.
[snip] 
> type 'a loc = {mutable contents : 'a} as {contents : 'a};;
[snip]
> This view conception of type exportation could also be generalized to
> hide some other information about a type to export: hide some
> constructors or labels...

Oh, my - if I could already think as fast ahead...

This looks indeed not bad and wouldn't even clutter the language! Programs
with elaborate record fields would surely benefit - no more read
access functions required (saves work both in the implementation and
the interface!)...

I am now waiting for Xavier to use his feared backhand to play back the
ball with another overlooked problem... ;-)

Best regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl