You could compile to brainfuck, treating it as a very simple virtual machine. It's just simplified to the point of being incredibly inefficient, like factoring

You could compile to brainfuck, treating it as a very simple virtual machine. It's just simplified to the point of being incredibly inefficient, like factoring Church-encoded numbers with Prolog's unification, rather than using its built-in mathematical primitives. (Whether the bf compiler was actually written or just generated by compiling to bf is neither here nor there.)