(defun split-components (forms)
  (loop :for cons :on forms
        :for form := (car cons)
        :if (symbolp (car form))
          :collect form :into components
        :else :do (loop-finish)
        :finally (return (values components cons))))

(defun process-component (component)
  (destructuring-bind (type . options/args) component
    (let* ((options-p (listp (first options/args)))
           (args (if options-p (rest options/args) options/args))
           (options (if options-p `(list ,@(first options/args)) '()))
           (accessors (loop :for (k v) :on args :by #'cddr
                            :nconc (list k `(lambda () ,v)) )))
      `(list ',type ,options ,@accessors))))

(defun process-entry (entry)
  (destructuring-bind ((name &rest options) &rest rest) entry
    (multiple-value-bind (components children) (split-components rest)
      `(list ',name ',options
             (list ,@(mapcar #'process-component components))
             (list ,@(mapcar #'process-entry children))))))

(defmacro define-prefab (name options &body data)
  (let ((entries `(((,name ,@options) ,@data))))
    `(list ,@(mapcar #'process-entry entries))))


(define-prefab foo ()
  ((a :template xxx)
   (foo1 :bar 2)
   (bar1 :bar 2)
   ((b)
    (foo2 :foo2 3)
    (bar2 :bar2 4))))

;; Expectations

(list
 (list 'foo nil nil
       (list
        (list 'a '(:template xxx)
              (list (list 'foo1 'nil :bar (lambda () 2))
                    (list 'bar1 'nil :bar (lambda () 2)))
              (list
               (list 'b nil
                     (list (list 'foo2 'nil :foo2 (lambda () 3))
                           (list 'bar2 'nil :bar2 (lambda () 4)))
                     nil))))))

;; Reality

(LIST
 (LIST 'FOO (LIST) (LIST)
       (LIST
        (LIST 'A (LIST :TEMPLATE XXX)
              (LIST (LIST 'FOO1 NIL :BAR (LAMBDA () 2))
                    (LIST 'BAR1 NIL :BAR (LAMBDA () 2)))
              (LIST
               (LIST 'B (LIST)
                     (LIST (LIST 'FOO2 NIL :FOO2 (LAMBDA () 3))
                           (LIST 'BAR2 NIL :BAR2 (LAMBDA () 4)))
                     (LIST)))))))