%---------------------------------------------------------------------------%
% vim: ts=4 sw=4 et ft=mercury
%---------------------------------------------------------------------------%
%
% Test the tracking of a subterm through an explicit supertree.

:- module explicit_subtree.

:- interface.

:- import_module io.

:- pred main(io::di, io::uo) is det.

:- implementation.

:- import_module exception.
:- import_module int.

main(!IO) :-
    p1(10, Q),
    io.write_int(Q, !IO),
    io.nl(!IO).

:- pred p1(int::in, int::out) is det.

p1(X, Y) :-
    p2(X, Y).

:- pred p2(int::in, int::out) is det.

p2(X, Y) :-
    p3(X, Y).

:- pred p3(int::in, int::out) is det.

p3(X, Y) :-
    calc(X, Y).

:- pred calc(int::in, int::out) is det.

calc(X, Y) :-
    ( if X > 0 then
        a(Z)
    else
        b(Z)
    ),
    divide2(X, Z, Y).

:- pred divide2(int::in, int::in, int::out) is det.

divide2(N, D, Q) :-
    ( if D = 0 then
        throw("zero denominator")
    else
        Q = N // D
    ).

:- pred b(int::out) is det.

b(-1).

:- pred a(int::out) is det.

a(X + Y - 100) :-
    q(49, 0, X),
    q(51, 0, Y).

:- pred q(int::in, int::in, int::out) is det.

q(A, B, C) :-
    ( if A =< 0 then
        B = C
    else
        q(A - 1, B + 1, C)
    ).