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;;; guile-2d
;;; Copyright (C) 2013 David Thompson <dthompson2@worcester.edu>
;;;
;;; Guile-2d 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.
;;;
;;; Guile-2d 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 program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Deferred procedure scheduling.
;;
;;; Code:
(define-module (2d agenda)
#:use-module (ice-9 q)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-26)
#:use-module (2d coroutine)
#:export (make-agenda
agenda?
agenda-time
tick-agenda!
clear-agenda!
schedule
schedule-interval
schedule-each
wait))
;; This code is a modified version of the agenda implementation in
;; SICP. Thank you, SICP!
;;;
;;; Time segment
;;;
(define-record-type <time-segment>
(%make-time-segment time queue)
time-segment?
(time segment-time)
(queue segment-queue))
(define (make-time-segment time . callbacks)
"Create a new time segment at TIME and enqueues everything in the
list CALLBACKS."
(let ((segment (%make-time-segment time (make-q))))
;; Enqueue all callbacks
(for-each (cut segment-enq segment <>) callbacks)
segment))
(define (segment-enq segment callback)
"Add the CALLBACK procedure to SEGMENT's queue."
(enq! (segment-queue segment) callback))
;;;
;;; Agenda
;;;
(define-record-type <agenda>
(%make-agenda time segments)
agenda?
(time agenda-time set-agenda-time!)
(segments agenda-segments set-agenda-segments!))
(define (make-agenda)
"Create a new, empty agenda."
(%make-agenda 0 '()))
(define (agenda-empty? agenda)
"Return #t if AGENDA has no scheduled procedures."
(null? (agenda-segments agenda)))
(define (first-segment agenda)
"Return the first time segment in AGENDA."
(car (agenda-segments agenda)))
(define (rest-segments agenda)
"Return everything but the first segment in AGENDA."
(cdr (agenda-segments agenda)))
(define (agenda-add-segment agenda time callback)
"Add a new time segment to the beginning of AGENDA at the given TIME
and enqueue CALLBACK."
(set-agenda-segments! agenda
(cons (make-time-segment time callback)
(agenda-segments agenda))))
(define (insert-segment segments time callback)
"Insert a new time segment after the first segment in SEGMENTS."
(set-cdr! segments
(cons (make-time-segment time callback)
(cdr segments))))
(define (first-agenda-item agenda)
"Return the first time segment queue in AGENDA."
(if (agenda-empty? agenda)
(error "Agenda is empty")
(segment-queue (first-segment agenda))))
(define (agenda-time-delay agenda dt)
"Return the sum of the time delta, DT, and the current time of AGENDA."
(+ (agenda-time agenda) (inexact->exact (round dt))))
(define (flush-queue! q)
"Dequeue and execute every member of Q."
(unless (q-empty? q)
((deq! q)) ;; Execute scheduled procedure
(flush-queue! q)))
(define (tick-agenda! agenda)
"Move AGENDA forward in time and run scheduled procedures."
(set-agenda-time! agenda (1+ (agenda-time agenda)))
(let next-segment ()
(unless (agenda-empty? agenda)
(let ((segment (first-segment agenda)))
;; Process time segment if it is scheduled before or at the
;; current agenda time.
(when (>= (agenda-time agenda) (segment-time segment))
(flush-queue! (segment-queue segment))
(set-agenda-segments! agenda (rest-segments agenda))
(next-segment))))))
(define (clear-agenda! agenda)
"Remove all scheduled procedures from AGENDA."
(set-agenda-segments! agenda '()))
(define* (schedule agenda thunk #:optional (delay 1))
"Schedule the procedure THUNK in AGENDA to be run DELAY ticks from
now. DELAY defaults to 1 if not specified."
(let ((time (agenda-time-delay agenda delay)))
(define (belongs-before? segments)
(or (null? segments)
(< time (segment-time (car segments)))))
(define (add-to-segments segments)
;; Add to existing time segment if the times match
(if (= (segment-time (car segments)) time)
(segment-enq (car segments) thunk)
;; Continue searching
(if (belongs-before? (cdr segments))
;; Create new time segment and insert it where it belongs
(insert-segment segments time thunk)
;; Continue searching
(add-to-segments (cdr segments)))))
(if (belongs-before? (agenda-segments agenda))
(agenda-add-segment agenda time thunk)
(add-to-segments (agenda-segments agenda)))))
(define (schedule-interval agenda thunk delay)
"Schedule THUNK within AGENDA to be applied every DELAY ticks."
(schedule agenda
(lambda ()
(thunk)
(schedule-interval agenda thunk delay))))
(define (schedule-each agenda thunk)
"Schedule THUNK within AGENDA to be applied every tick."
(schedule-interval agenda thunk 1))
(define (wait agenda delay)
"Yield coroutine and schedule the continuation to be run after DELAY
ticks."
(yield (cut schedule agenda <> delay)))
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