From: Michael Wohlwend <micha-1@fantasymail.de>
> that code :
[..]
> causes this exception:
> Fatal error: exception Ctype.Unify(_, 0)
> (Program not linked with -g, cannot print stack backtrace)

This should be a bug report :-)
Indeed, the problem seems to be still there on the 3.08 branch after
3.08.4.
On the other, this bug does not appear on the 3.09 branch, which is to
be released real soon now. (I hope.)
I'll try to look into this.

Jacques Garrigue