%---------------------------------------------------------------------------%
% vim: ts=4 sw=4 et ft=mercury
%---------------------------------------------------------------------------%

:- module unify_inst_bug.
:- interface.

:- type t(T)
    --->    ta
    ;       tb(t(t(T))).
:- inst t(T)
    --->    ta
    ;       tb(t(t(T))).

:- mode m == in(t(ground)).

:- pred p(t(int)::m, t(int)::m) is semidet.

:- implementation.

% XXX The following code attempts to abstractly unify the inst t(ground)
% with itself. Since types have been propagated into the modes, each level
% of the inst tree contains a new type that has never been referred to before
% (t(int), t(t(int)), t(t(t(int))), etc). Therefore the abstract unification
% never terminates.

p(X, X).