%------------------------------------------------------------------------------%

:- module polymorphism_try_bug.

:- interface.

:- import_module io.

:- type bexpr(V) --->
    bexpr(V).

:- pred test(bexpr(Var)::in, io::di, io::uo) is det.

:- pred test2(bexpr(Var)::in, io::di, io::uo) is det.

:- implementation.

:- import_module maybe.
:- import_module require.

:- type bdd(V) --->
    bdd(V).

test(BooleanExpression, !IO) :-
    promise_equivalent_solutions [MaybeBDD] (
    ( try []
        BDDPrime = make_bdd(BooleanExpression)
      then
        MaybeBDD = ok(BDDPrime)
      catch_any ExpPrime ->
        MaybeBDD = error({"My error message", ExpPrime})
    )),
    ( MaybeBDD = ok(BDD)
    ; MaybeBDD = error({ErrMessage, _}),
        write_string(ErrMessage, !IO),
        sorry($pred, "Error")
        % throw(Exp) % This also causes the bug.
    ),

    io.write(BDD, !IO).


% This version of the same code uses a type rather than a tuple, it has the
% same problem.

:- type my_pair(A, B) --->
    my_pair(A, B).

test2(BooleanExpression, !IO) :-
    promise_equivalent_solutions [MaybeBDD] (
    ( try []
        BDDPrime = make_bdd(BooleanExpression)
      then
        MaybeBDD = ok(BDDPrime)
      catch_any ExpPrime ->
        MaybeBDD = error(my_pair("My error message", ExpPrime))
    )),
    ( MaybeBDD = ok(BDD)
    ; MaybeBDD = error(my_pair(ErrMessage, _)),
        write_string(ErrMessage, !IO),
        sorry($pred, "Error")
        % throw(Exp) % This also causes the bug.
    ),

    io.write(BDD, !IO).

:- func make_bdd(bexpr(V)) = bdd(V).

make_bdd(bexpr(V)) = bdd(V).