:- module bug402.
:- interface.

:- type foo
    --->    foo
    ;       bar
    ;       baaz.

:- pred convert(foo::in, foo::out) is semidet.

:- implementation.

convert(!Value) :-
    require_complete_switch [!.Value] (
        !.Value = foo,
        !:Value = bar
    ;
        !.Value = bar,
        false
    ;
        !.Value = baaz,
        !:Value = foo
    ).