[m-users.] A neater way to call chained init functions?

[emacstheviking]

Given these three library init predicates...

:- pred setup_sdl(bool::out, io::di, io::uo) is det.
:- pred setup_sdlmix(bool::out, io::di, io::uo) is det.
:- pred setup_sdlimg(bool::out, io::di, io::uo) is det.

is there a more idiomatic / efficient / less $%^&*( ugly way to do this
please...

:- pred setup_app(bool::out, io::di, io::uo) is det.

setup_app(CanRun, !IO) :-
    setup_sdl(SdlUp, !IO),
    (
        SdlUp = yes,
        setup_sdlimg(ImgUp, !IO),
        (
            ImgUp = yes,
            setup_sdlmix(MixUp, !IO),
            (
                MixUp = yes,
                CanRun = yes
            ;
                MixUp = no,
                CanRun = no
            )
        ;
            ImgUp = no,
            CanRun = no
        )
    ;
        SdlUp = no,
        CanRun = no
    ).

 IIUIC you can't have predicates being anything other than `det` if they
use IO ? The above code is classic staircase, in Haskell I'd hear "maybe
monads" screaming at me but I have not yet gotten exposure to the std_util
maybe wrapper...it seems to be just a normal type constructor with yes(T)
and no, and also maybe_error as well. All suggestions welcome!!

 It's going well, I have sounds, images, lines, rectangles all in a window
but I am now trying to get away from the FFI and start to learn more
idiomatic Mercury.

 Thanks,
 Sean
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