anchor.diff:  (defparameter *in-struct* nil)
   
   (defun composite-literal (type value)
  +  (when (typep value '(cons (eql :literal)))
  +    ;; don't wrap things that are already literals
  +    (return-from composite-literal value))
     (etypecase type
       (scalar
        `(:literal ,type ,value))
  
positive.code:           (list* (car *current-form*) id type
                   :decorate decorate :default default
                   (when layout (list :layout layout))))))
  
  (defpass1 input (id type &key decorate default)
    (pass1/variable :input id type decorate default))
  
negative.code:      (spirv-core:branch @53)
       (spirv-core:label @53)
       (spirv-core:load %54 :int i)
       (literal %l4 :int 4) ;; alternate syntax for literals
       (spirv-core:s-less-than %56 :bool %54 %l4) ; i < 4
       (spirv-core:branch-conditional %56 @50 @51) ; body or break
       (spirv-core:label @50)                      ; body
       (spirv-core:load %58 :vec4 multiplier)
  