(in-package :data-lens.transducers.internals)
 
 (defgeneric reduce-generic (seq func init)
   (:method ((seq sequence) (func function) init)
     (reduce func seq :initial-value init))
   (:method ((seq sequence) (func symbol) init)
     (reduce func seq :initial-value init))
   (:method (seq (func symbol) init)
     (reduce-generic seq
                     (symbol-function func)
                     init))
   (:method ((seq hash-table) (func function) init)
     (let ((acc init))
       (maphash (lambda (k v)
                  (setf acc (funcall func acc (list k v))))
                seq)
       acc)))

 
 (defgeneric init (client))
 (defgeneric stepper (client))
 (defgeneric unwrap (client obj)
   (:method (client obj) obj))
 
 (defun exit-early (acc)
   (throw 'done acc))
 
 (defun transduce (xf build seq)
   (let* ((xf (etypecase xf
                (list (apply 'alexandria:compose xf))
                ((or function symbol) xf)))
          (transducer (funcall xf (stepper build))))
     (unwrap build
             (funcall transducer
                      (catch 'done
                        (reduce-generic seq
                                        transducer
                                        (init build)))))))
 
 #+(or)
 (defdocumentation transducer-protocol
     (:function transduce (xf build seq)
                )
   (:generic-function unwrap (client obj)
                      )
   (:generic-function unwrap (client obj)
                      )
   (:generic-function unwrap (client obj)
                      ))