anchor.diff:  ; bender – Copyright (c) 2014–2015 Sven Michael Klose <pixel@copei.de>
   
   (defun assemble-expression (x &key (ensure? nil) (not-zero? nil))
  -  (| (& (number? x) x)
  +  (| (? (| (number? x)
  +           (string? x))
  +        x)
        (case x.
          'expression  (unless (& (not ensure?)
                                  (first-pass?))
  
positive.code:      (unless not-zero?
         0)))
  
  (def-instruction assemble-operand (instruction x)
    (when (character? x)
      (= operand (char-code x)))
    (when (eq 'branch addrmode)
      (= x (- x *pc* 1))
      (& (< 2 *pass*)
  
negative.code: (defun assemble-instruction (instruction)
    (= (instruction-address instruction) *pc*)
    (= (instruction-operand instruction)
       (assemble-operand instruction (assemble-expression (instruction-operand-expression instruction))))
    (instruction-optimize-addrmode instruction)
    instruction)
  
  