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Diffstat (limited to '2d/agenda.scm')
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1 files changed, 182 insertions, 0 deletions
diff --git a/2d/agenda.scm b/2d/agenda.scm new file mode 100644 index 0000000..ca23dac --- /dev/null +++ b/2d/agenda.scm @@ -0,0 +1,182 @@ +;;; 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) + #:export (make-agenda + with-agenda + agenda-schedule + update-agenda + clear-agenda)) + +;; 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) + "Constructs a new time segment with given time and enqueus all +callback procedures." + (let ((segment (%make-time-segment time (make-q)))) + ;; Enqueue all callbacks + (for-each (lambda (c) (segment-enq segment c)) callbacks) + segment)) + +(define (segment-enq segment callback) + "Enqueues a callback procedure onto the segment 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) + "Creates a new empty agenda." + (%make-agenda 0 '())) + +;; The global agenda that will be used when schedule is called outside +;; of a with-agenda form. +(define global-agenda (make-agenda)) + +(define *current-agenda* global-agenda) + +;; emacs: (put 'with-agenda 'scheme-indent-function 1) +(define-syntax-rule (with-agenda agenda body ...) + (begin + (set! *current-agenda* agenda) + body + ... + (set! *current-agenda* global-agenda))) + +(define (agenda-empty? agenda) + "Returns #t if agenda has no scheduled procedures." + (null? (agenda-segments agenda))) + +(define (first-segment agenda) + "Returns the first time segment in the agenda." + (car (agenda-segments agenda))) + +(define (rest-segments agenda) + "Returns everything but the first segment in the agenda." + (cdr (agenda-segments agenda))) + +(define (agenda-add-segment agenda time callback) + "Adds a new time segment to the beginning of the agenda and enqueues +the given callback." + (set-agenda-segments! agenda (cons (make-time-segment time callback) + (agenda-segments agenda)))) + +(define (insert-segment segments time callback) + "Inserts a new segment after the first segment in the list." + (set-cdr! segments (cons (make-time-segment time callback) (cdr segments)))) + +(define (first-agenda-item agenda) + "Returns the first time segment queue in the agenda." + (if (agenda-empty? agenda) + (error "Agenda is empty") + (segment-queue (first-segment agenda)))) + +(define (agenda-time-delay agenda dt) + "Returns time given a delta from the current agenda time." + (+ (agenda-time agenda) (inexact->exact (round dt)))) + +(define (%agenda-schedule agenda callback dt) + "Schedules a callback procedure in the agenda relative to the +current agenda time." + (let ((time (agenda-time-delay agenda dt))) + (define (belongs-before? segments) + "Determines if the time segment belongs before the first segment +in the list" + (or (null? segments) + (< time (segment-time (car segments))))) + + (define (add-to-segments segments) + "Schedules callback in the proper place." + ;; Add to existing time segment if the times match + (if (= (segment-time (car segments)) time) + (segment-enq (car segments) callback) + ;; Continue searching + (if (belongs-before? (cdr segments)) + ;; Create new time segment and insert it where it belongs + (insert-segment segments time callback) + ;; Continue searching + (add-to-segments (cdr segments))))) + + ;; Handle the case of inserting a new time segment at the + ;; beginning of the segment list. + (if (belongs-before? (agenda-segments agenda)) + ;; Add segment if it belongs at the beginning of the list... + (agenda-add-segment agenda time callback) + ;; ... Otherwise, search for the right place + (add-to-segments (agenda-segments agenda))))) + +(define (flush-queue! q) + "Dequeues and executes every element of q." + (unless (q-empty? q) + ((deq! q)) ;; Execute scheduled procedure + (flush-queue! q))) + +(define (%update-agenda agenda) + "Moves 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) + "Removes all scheduled procedures from the agenda." + (set-agenda-segments! agenda '())) + +(define* (agenda-schedule thunk #:optional (delay 1)) + "Schedules thunk in the current agenda." + (%agenda-schedule *current-agenda* thunk delay)) + +(define (update-agenda) + "Updates the current agenda." + (%update-agenda *current-agenda*)) + +(define (clear-agenda) + "Clears the current agenda." + (%clear-agenda *current-agenda*)) |