I recently needed to make a cross platform assembler for a niche 8-bit micro that only has DOS tooling. After cloning it in a small bit of Python I was looking for a simple way to extend it with macros. It turns out that m4 works really well as an asm macro language and I now have advanced facilities like a code generating expression evaluator and high level control flow statements without any significant change to the core assembler. It blows the doors off what contemporary assemblers (nasm, masm, tasm) can do and hearkens back to the high point of high level assemblers when they peaked in the 70s.