anchor.diff:  
   (add-op-after spirv-core:ext-inst-import (dest name)
     (use-extension dest name))
  +
  +(add-op-after spirv-core:capability (cap)
  +  (setf (gethash cap *enabled-caps*) t))
   
   (add-op-after spirv-core:variable (id type storage-class
                                         &optional initial-value)
  
positive.code: (defvar *current-section*) ;; bind to 1
  ;; just for debugging
  (defvar *current-form* nil)
  (defvar *id-conflicts*)
  
  (defmacro with-ll-asm-context (() &body body)
    `(let ((*next-id* 0)
  
negative.code:                         ,@(unless operands
                              `((declare (ignore args))))
                          ,@(loop for cap in required-capabilities
                                  collect `(check-cap ,cap))
                          (with-spirv-instruction (,ext-inst)
                            (asm-type type)
                            (asm-id dest)
  