A C++ Template Meta Brainfuck Interpreter

For practise reasons, i implemented this Brainfuck Interpreter on a long train ride. It works completely at compile time, as it is implemented in a purely functional way, expressed in C++ Template Language.

The program and user input is provided via type lists, and the output is a type list again. The output string, as well as the Brainfuck Machine state can be printed as a compiler error message. Of course, it would also be possible to write code which prints the output on the terminal, when the compiled program is being run.

Usage

The program is encoded like this in the source code:

    using input_list = char_tl_t<'a', 'b', 'c'>;
    using prog       = char_tl_t<'+', '+', '+', '[', '.', '-', ']'>;

    using BFM = bfm::io_bfm<bfm::make_t, input_list, tl::null_t>;

    debug_t<bfm::run_tm_t<BFM, prog>::output> t;

The following is the (barely readable, but correct) output:

Jacek.Galowicz ~/src/tmp_brainfuck $ g++ -o main main.cpp -std=c++14
main.cpp:17:47: error: implicit instantiation of undefined template 'debug_t<tl::tl<char_t<'\x03'>, tl::tl<char_t<'\x02'>, tl::tl<char_t<'\x01'>, tl::null_t> > > >'
    debug_t<bfm::run_tm_t<BFM, prog>::output> t;
                                              ^
main.cpp:8:29: note: template is declared here
template <typename T> class debug_t;
                            ^
1 error generated.