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% vim: ts=4 sw=4 et ft=mercury
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:- module double_error.

:- interface.

:- import_module io.

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

:- implementation.

:- import_module list.
:- import_module require.

main -->
    io__command_line_arguments(Args),
    { list__length(Args, Num) },
    (
        { p(Num) }
    ->
        io__write_string("1\n")
    ;
        { Arg = "not 1\n" },
        { error(Arg) }
    ),
    (
        { q(Num) }
    ->
        io__write_string("2\n")
    ;
        { Arg = "not 2\n" },
        { error(Arg) }
    ).

:- pred p(int::in) is semidet.

p(0).
p(1).
p(2).
p(3).

:- pred q(int::in) is semidet.

q(0).
q(4).
q(5).
q(6).