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74 lines
1.7 KiB
Mathematica
74 lines
1.7 KiB
Mathematica
%---------------------------------------------------------------------------%
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% vim: ts=4 sw=4 et ft=mercury
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%---------------------------------------------------------------------------%
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:- module checked_nondet_tailcall.
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:- interface.
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:- import_module io.
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:- pred main(io::di, io::uo) is det.
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:- implementation.
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:- import_module list.
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:- import_module solutions.
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main(!IO) :-
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join(1, Ones),
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write_ints(Ones, !IO),
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join(2, Twos),
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write_ints(Twos, !IO),
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join(3, Threes),
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write_ints(Threes, !IO),
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join(4, Fours),
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write_ints(Fours, !IO),
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join(5, Fives),
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write_ints(Fives, !IO).
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:- pred edge1(int::in, int::out) is nondet.
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edge1(1, 11).
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edge1(1, 12).
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:- pred edge2(int::in, int::out) is nondet.
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edge2(11, 18).
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edge2(12, 19).
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edge2(2, 21).
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edge2(2, 22).
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edge2(3, 31).
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edge2(4, 41).
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:- pred edge12(int::in, int::out) is nondet.
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edge12(A, B) :-
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( if edge1(A, C) then
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% When we come here after the last success of edge1,
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% the call to edge2 will be a checked nondet tailcall.
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% When we come here after a non-last success of edge1,
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% the check will fail, and we will have to do a
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% non-tail call.
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D = C
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else
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% When this arm of the switch is taken, the call to edge2
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% will be a checked nondet tailcall.
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D = A
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),
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edge2(D, B).
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:- pred join(int::in, list(int)::out) is det.
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join(A, Bs) :-
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solutions((pred(B::out) is nondet :- edge12(A, B)), Bs).
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:- pred write_ints(list(int)::in, io::di, io::uo) is det.
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write_ints([], !IO) :-
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io.write_string("\n", !IO).
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write_ints([X | Xs], !IO) :-
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io.write_int(X, !IO),
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io.write_string(" ", !IO),
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write_ints(Xs, !IO).
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