hutch (and jj2007),
Thank you both for the replies. As soon as I read jj's reply I hit the 'net and looked up lexer/parser. At first it seemed exciting--tons of sites with info on the subject. Trouble is, I'm not a C/Java/etc. programmer. For me, it's been literally assembler since the late 70s. So immediately I felt overwhelmed. Granted, I had to pick up some C to understand most of Windows, but I certainly cannot program much past "Hello World" in those languages. I'm still going to do this, but it might be writing the parser using lookup tables (or something along those lines that I'm comfortable with). Before getting excited about Google, that was the direction I was headed. It will be a month of Sundays before I understand the HLL code that's out there for those parsing engines. It could be longer than that.
I guess I was hoping there might be someone reading who had done this sort of thing in assembly before and who might be willing to throw a tip my way as to how they did it. Lots of talent around this place and I'm wide-open for ideas from anyone.
So, for now I'll keep reading source code from some of the assemblers that are out there, maybe adapt some 6502/816 native assembler source, and work on the code I have now (which is reading line by line from a source file loaded into RAM and, so far, roughly seems to work), and see what happens. Eventually it will fall into place. Regardless, it will never need to be as complicated as something like MASM--it's destined for the c64. Macros, nested include files, structures, and conditional assembly are about all the fancy it needs for now. I am reading about compiler design, though, and that is already helping with the organizational aspect.
Thanks again to both of you.