Advent of Code Day 7 Part 1 and Part 2 (code only solves Part 2)

aoc_7.erl

-module(aoc).

-export([main/1]).

main([Path]) ->
  {ok, Content} = file:read_file(Path),
  Data = parse(Content),
  io:format("Result: ~p~n", [lists:sum(lists:map(fun test/1, Data))]),
  erlang:halt(0).

parse(Bin) when is_binary(Bin) ->
  lists:map(fun(Line) ->
    [R,Rest] = binary:split(Line, <<":">>, [global, trim_all]),
    I = lists:map(fun(B) ->
      binary_to_integer(B)
    end, binary:split(Rest, <<" ">>, [global, trim_all])),
    {binary_to_integer(R), I}
  end, binary:split(Bin, <<"\n">>, [global, trim_all])).

calc(add, A, B) -> A + B;
calc(mult, A, B) -> A * B;
calc(concat, A, B) ->
  AB = integer_to_binary(A),
  BB = integer_to_binary(B),
  binary_to_integer(<<AB/binary, BB/binary>>).

build(N) -> build(N, 0, nil).

build(N, I, C) when I == N -> C;
build(N, I, C) -> build(N, I+1, expand(C)).

expand(A) when is_atom(A) -> {A,add,mult,concat};
expand({Op, nil, nil}) -> {Op,add,mult,concat};
expand({Op,N1,N2,N3}) -> {Op,expand(N1),expand(N2),expand(N3)}.

test({Result,[H|T]}) ->
  case test(Result, T, build(length([H|T]) - 1), H) of
    true -> Result;
    false -> 0
  end.

test(Result, [], _, Acc) -> Result == Acc;
test(Result, [H|T], {nil,A,B,C}, Acc) ->
  test(Result, [H|T], A, Acc) orelse
    test(Result, [H|T], B, Acc) orelse
      test(Result, [H|T], C, Acc);
test(Result, [H|T], {Op,A,B,C}, Acc) ->
  case Acc > Result of
    true -> false;
    false ->
      test(Result, T, A, calc(Op, Acc, H)) orelse
        test(Result, T, B, calc(Op, Acc, H)) orelse
          test(Result, T, C, calc(Op, Acc, H))
  end;
test(Result, [H|T], Op, Acc) -> test(Result, T, nil, calc(Op, Acc, H)).