:- module basics.
:- interface.
:- import_module io.

:- type part ---> one; two.
:- pred part(string, part).
:- mode part(in,  out) is semidet.
:- mode part(out, in)  is det.

:- func part(part, T, T) = T.

:- type answer ---> int(int); string(string); lines(list(string)).
:- pred output(answer::in, io::di, io::uo) is det.


:- func ite((pred), T, T) = T.
:- mode ite((pred) is semidet, in, in) = out is det.


:- import_module list.
:- import_module string.

:- type lines == list(string).

:- pred die(string::in) is erroneous.
:- pred die(string::in, list(poly_type)::in) is erroneous.

:- pred need(io.res(T)::in, T::out) is det.
:- pred read_lines_need(string::in, lines::out, io::di, io::uo) is det.


:- pred wrap_main(pred(io, io), io, io).
:- mode wrap_main(pred(di, uo) is cc_multi, di, uo) is cc_multi.
:- mode wrap_main(pred(di, uo) is det,      di, uo) is cc_multi.


:- import_module char.

:- type chars == list(char).


:- import_module int.

:- func sum(list(int)) = int.
:- func replicate(int, T) = list(T).

:- func map_index(func(int, T) = U, list(T)) = list(U).


:- import_module maybe.

:- func to_int_may(string) = maybe(int).


:- implementation.

part("1", one).
part("2", two).

part(one, X, _) = X.
part(two, _, Y) = Y.


output(int(I),    !IO) :- write_int(I, !IO), nl(!IO).
output(string(S), !IO) :- write_string(S, !IO), nl(!IO).
output(lines(Ss), !IO) :- write_list(Ss, "\n", write_string, !IO), nl(!IO).


ite(P, T, E) = X :- if P then X = T else X = E.


:- import_module exception.

:- type die ---> death(string).

die(Str) :- throw(death(Str)).
die(Fmt, Args) :- die(format(Fmt, Args)).

wrap_main(Main, !IO) :-
  try [io(!IO)] Main(!IO)
  then true
  catch death(Err) -> (
    format("%s\n", [s(Err)], !IO),
    set_exit_status(1, !IO)
  ).

need(ok(X),    X).
need(error(E), _) :- die(error_message(E)).

read_lines_need(File, Lines, !IO) :-
  read_named_file_as_lines(File, Res, !IO),
  need(Res, Lines).


sum(Xs) = foldl(plus, Xs, 0).

replicate(N, X) = Out :-
  if N = 0 then Out = [] else Out = [X | replicate(N - 1, X)].

:- func map_index(int, func(int, T) = U, list(T)) = list(U).
map_index(_, _, [])       = [].
map_index(I, F, [X | Xs]) = [F(I, X) | map_index(I+1, F, Xs)].

map_index(F, Xs) = map_index(0, F, Xs).


to_int_may(Str) = Out :-
  if to_int(Str, N) then Out = yes(N) else Out = no.