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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:
+;;
+;; Time-based signals.
+;;
+;;; Code:
+
+(define-module (2d time)
+  #:use-module (2d agenda)
+  #:use-module (2d signals)
+  #:export (time-every
+            time-interval
+            time-delay))
+
+(define (time-interval ticks)
+  "Create a new signal that sets its value to #t every TICKS agenda
+updates."
+  (let ((signal (make-signal #:init #t)))
+    (agenda-schedule-interval
+     (lambda ()
+       (signal-set! signal #t)) ticks)
+    signal))
+
+(define (time-every)
+  "Create a new signal that sets its value to #t every agenda update."
+  (time-interval 1))
+
+(define (time-delay ticks signal)
+  (make-signal
+   #:filter (lambda (value old from)
+              (wait ticks)
+              #t)
+   #:connectors (list signal)))