anchor.diff:        (case x.. :test #'eq
           'label       (. x. (parse-0 .x))
           'directive   (parse-directive x)
  -        'mnemonic    (with ((addrmode operand-expression) (parse-operand .x))
  -                       (list (make-instruction :mnemonic x..
  -                                               :addrmode addrmode
  -                                               :operand-expression operand-expression)))
  +        'mnemonic    (parse-instruction x)
           (? (identifier? x.)
              (? (assignment? .x.)
                 (parse-assignment x)
  
positive.code: (defun parse-directive (x)
    `((,(car x.) ,(cdr x.) ,@.x)))
  
  (defun parse-0 (x)
    (when x
      (?
  
negative.code:     (eq 'hash x..)
        (progn
          (| (number-or-identifier? .x.)
             (parser-error "Expression expected instead of ~A."
                           (car .x.)))
          (values 'imm .x.))
      (number-or-identifier? x.)
        (? (not .x)
  