anchor.diff:                                                implicit-args))
                                              nil ;;{TODO} should be context
                                              arg-types
  -                                           (return-set body-obj)
  +                                           (or (return-set body-obj)
  +                                               (make-type-set))
                                              :code (list raw-args body)
                                              :glsl-name glsl-name
                                              :implicit-args implicit-args
  
positive.code:                                return-for-glsl body-obj
                                 implicit-args in-out-args)))
               (arg-types (mapcar #'second args))
               (func (make-user-function-obj name
                                             (unless strip-glsl
                                               (gen-function-transform
  
negative.code:                                                        (flow-ids (elt (return-set body-obj) 0)))
                                             :in-arg-flow-ids in-arg-flow-ids
                                             :pure (pure-p body-obj)))
               (tl-meta (hash-table-values (slot-value body-env 'local-metadata)))
               (code-obj (copy-compiled body-obj
                                        :type-set (make-type-set)
  