ia65 is an interactive assembler for the Mite 6502 project. I've been
doing my assembly work via a cross-assembler but now I want a self-
hosted assembler to run on the Mite board itself.

Current state:

  * all NMOS 6502 and most CMOS 65C02 opcodes supported
  * .ORG, .EQU, .BYTE, .WORD directives supported
  * labels up to 14 characters (but no forward references)
  * all numbers in hexadecimal


So this should work, for example:

  PRCH .EQU $CD04

  ;; Execute a basic loop
  INIT
    LDA #30
    LDY #10
  LOOP
    JSR PRCH       ; print character
    INC
    DEY
    BNE LOOP

As a special case, the format "LABEL=value" is also recognised.

Simple expressions are supported. > and < are prefix operators
selecting the upper and lower bytes of a word, respectively, and
! is a prefix negation. &, |, + and - can be used on operand values.
No multiplication, division, or shifts. Operators are evaluated
left-to-right with no precedence.


What's missing?
  * decimal and binary values
  * single-pass with no resolution of undefined labels