:- module bug.
:- interface.

:- type tt(T) ---> tt.

:- typeclass tc(T) where [].
:- instance tc(tt(_)).

:- func myfunc(T) = int <= tc(T).
:- pragma type_spec(myfunc/1, T = tt(_)).

:- implementation.

:- instance tc(tt(_)) where [].

myfunc(_) = 0.