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:- module match_append_impl.

:- interface.

:- import_module char.
:- import_module list.

:- pred match_aab(list(char)::in) is semidet.

:- implementation.

match_aab(S) :-
    match([a, a, b], S).

:- pred match(list(char)::in, list(char)::in) is semidet.

match(P, S) :-
    app(S1, _, S),
    app(_, P, S1).

:- pred app(list(char), list(char), list(char)).
:- mode app(in, in, out) is det.
:- mode app(in, out, in) is semidet.
:- mode app(out, out, in) is multi.
:- mode app(out, in, in) is nondet. % actually semidet.

app([], L, L).
app([H | L1], L2, [H | L3]) :-
    app(L1, L2, L3).