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;; Copyright (C) 2020 Free Software Foundation, Inc.
;;
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 3 of the License, or (at your option) any later version.
;;
;; This library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library; if not, write to the Free Software
;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
(define-module (srfi srfi-171 gnu)
#:use-module (srfi srfi-171)
#:use-module (srfi srfi-171 meta)
#:export (tbatch tfold))
(define tbatch
(case-lambda
((reducer)
(tbatch identity reducer))
((t r)
(lambda (reducer)
(let ((cur-reducer (t r))
(cur-state (r)))
(case-lambda
(() (reducer))
((result)
(if (equal? cur-state (cur-reducer))
(reducer result)
(let ((new-res (reducer result (cur-reducer cur-state))))
(if (reduced? new-res)
(reducer (unreduce new-res))
(reducer new-res)))))
((result value)
(let ((val (cur-reducer cur-state value)))
(cond
;; cur-reducer is done. Push value downstream
;; re-instantiate the state and the cur-reducer
((reduced? val)
(let ((unreduced-val (unreduce val)))
(set! cur-reducer (t r))
(set! cur-state (cur-reducer))
(reducer result (cur-reducer unreduced-val))))
(else
(set! cur-state val)
result))))))))))
(define* (tfold reducer #:optional (seed (reducer)))
(lambda (r)
(let ((state seed))
(case-lambda
(() (r))
((result) (r result))
((result value)
(set! state (reducer state value))
(if (reduced? state)
(reduced (reducer (unreduce state)))
(r result state)))))))
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