Metaprogramming

Instead of using an external filter that expands macros, one way to do things is to write programs that write part or all of other programs.

For instance, you could use a program outputting source code

Think about it!

Backends from compilers

Compilers like GCC, SML/NJ, Objective CAML, MIT-Scheme, CMUCL, etc, do have their own generic assembler backend, which you might choose to use, if you intend to generate code semi-automatically from the according languages, or from a language you hack: rather than write great assembly code, you may instead modify a compiler so that it dumps great assembly code!

The New-Jersey Machine-Code Toolkit

There is a project, using the programming language Icon (with an experimental ML version), to build a basis for producing assembly-manipulating code. See around http://www.eecs.harvard.edu/~nr/toolkit/

TUNES

The TUNES Project for a Free Reflective Computing System is developing its own assembler as an extension to the Scheme language, as part of its development process. It doesn't run at all yet, though help is welcome.

The assembler manipulates abstract syntax trees, so it could equally serve as the basis for a assembly syntax translator, a disassembler, a common assembler/compiler back-end, etc. Also, the full power of a real language, Scheme, make it unchallenged as for macroprocessing/metaprogramming.