Add current-agenda parameter.

* 2d/agenda.scm (current-agenda): New variable.
  (with-agenda): New macro.
  (agenda-time, tick-agenda!, clear-agenda!, schedule)
  (schedule-interval, schedule-each, wait): Remove agenda parameter.

* 2d/game.scm (game-agenda): Delete it.
  (update): Tick current agenda.

* 2d/helpers.scm (define-guardian): Remove agenda argument.

* 2d/repl.scm (start-2d-repl): Remove agenda argument to schedule-each.

* 2d/signal.scm (signal-sample, signal-delay, signal-throttle): Remove
  agenda parameter.

* 2d/sprite.scm:
* examples/common.scm:
* examples/coroutine.scm:
* examples/font.scm:
* examples/particles.scm: Remove mention of game-agenda.

* README.org: Update example snippets.

11 files changed, 99 insertions, 75 deletions

diff --git a/2d/agenda.scm b/2d/agenda.scm
index a0a6fb3..ab36f23 100644
--- a/2d/agenda.scm
+++ b/2d/agenda.scm
@@ -30,6 +30,8 @@
   #:export (make-agenda
             agenda?
             agenda-time
+            current-agenda
+            with-agenda
             tick-agenda!
             clear-agenda!
             schedule
@@ -69,7 +71,7 @@ list CALLBACKS."
 (define-record-type <agenda>
   (%make-agenda time segments)
   agenda?
-  (time agenda-time set-agenda-time!)
+  (time %agenda-time set-agenda-time!)
   (segments agenda-segments set-agenda-segments!))
 
 (define (make-agenda)
@@ -109,7 +111,7 @@ and enqueue CALLBACK."
 
 (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))))
+  (+ (%agenda-time agenda) (inexact->exact (round dt))))
 
 (define (flush-queue! q)
   "Dequeue and execute every member of Q."
@@ -117,26 +119,25 @@ and enqueue CALLBACK."
     ((deq! q)) ;; Execute scheduled procedure
     (flush-queue! q)))
 
-(define (tick-agenda! agenda)
+(define (%tick-agenda! agenda)
   "Move AGENDA forward in time and run scheduled procedures."
-  (set-agenda-time! agenda (1+ (agenda-time agenda)))
+  (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))
+        (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)
+(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."
+(define (%schedule agenda thunk delay)
+  "Schedule THUNK to be run after DELAY ticks of AGENDA."
   (let ((time (agenda-time-delay agenda delay)))
     (define (belongs-before? segments)
       (or (null? segments)
@@ -157,19 +158,49 @@ now.  DELAY defaults to 1 if not specified."
         (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))
-            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)))
+(define current-agenda
+  (make-parameter (make-agenda)
+                  (lambda (val)
+                    (if (agenda? val)
+                        val
+                        (error "Must be an agenda")))))
+
+(define-syntax-rule (with-agenda agenda body ...)
+  (parameterize ((current-agenda agenda))
+    body ...))
+
+(define (agenda-time)
+  "Return the time of the current agenda."
+  (%agenda-time (current-agenda)))
+
+(define (tick-agenda!)
+  "Increment time for the current agenda and run scheduled
+procedures."
+  (%tick-agenda! (current-agenda)))
+
+(define (clear-agenda!)
+  "Remove all scheduled procedures from the current agenda."
+  (%clear-agenda! (current-agenda)))
+
+(define* (schedule thunk #:optional (delay 1))
+  "Schedule THUNK to be applied after DELAY ticks of the current
+agenda, or 1 tick if DELAY is not specified."
+  (%schedule (current-agenda) thunk delay))
+
+(define (schedule-interval thunk interval)
+  "Schedule THUNK to be applied every INTERVAL ticks of the current
+agenda."
+  (coroutine
+   (while #t
+     (wait interval)
+     (thunk))))
+
+(define (schedule-each thunk)
+  "Schedule THUNK to be applied upon every tick of the current
+agenda."
+  (schedule-interval thunk 1))
+
+(define (wait delay)
+  "Abort coroutine and schedule the continuation to be run after DELAY
+ticks of the current agenda."
+  (yield (cut schedule <> delay)))
diff --git a/2d/game.scm b/2d/game.scm
index befe784..d6a0345 100644
--- a/2d/game.scm
+++ b/2d/game.scm
@@ -32,7 +32,6 @@
   #:use-module (2d window)
   #:export (tick-interval
             max-ticks-per-frame
-            game-agenda
             draw-hook
             start-game-loop
             stop-game-loop))
@@ -49,7 +48,6 @@
 ;; completely unresponsive and possibly crashing.
 (define max-ticks-per-frame 4)
 (define draw-hook (make-hook 2))
-(define game-agenda (make-agenda))
 
 (define (draw dt alpha)
   "Render a frame."
@@ -68,7 +66,7 @@ is the unused accumulator time."
     (cond ((>= ticks max-ticks-per-frame)
            lag)
           ((>= lag tick-interval)
-           (tick-agenda! game-agenda)
+           (tick-agenda!)
            (iter (- lag tick-interval) (1+ ticks)))
           (else
            lag)))
diff --git a/2d/helpers.scm b/2d/helpers.scm
index 18bf8fa..59633d6 100644
--- a/2d/helpers.scm
+++ b/2d/helpers.scm
@@ -45,10 +45,9 @@ within the guardian is GC'd.  Reaping is ensured to happen from the
 same thread that is running the game loop."
   (begin
     (define name (make-guardian))
-    (schedule-interval game-agenda
-                       (lambda ()
-                         (let reap ((obj (name)))
-                           (when obj
-                             (reaper obj)
-                             (reap (name)))))
-                       1)))
+    (schedule-each
+     (lambda ()
+       (let reap ((obj (name)))
+         (when obj
+           (reaper obj)
+           (reap (name))))))))
diff --git a/2d/repl.scm b/2d/repl.scm
index 02237b6..f48b6d2 100644
--- a/2d/repl.scm
+++ b/2d/repl.scm
@@ -25,7 +25,6 @@
   #:use-module (system repl coop-server)
   #:use-module (system repl server)
   #:use-module (2d agenda)
-  #:use-module (2d game)
   #:export (start-2d-repl))
 
 (define* (start-2d-repl #:optional (port (make-tcp-server-socket #:port 37146)))
@@ -33,6 +32,6 @@
 default, this port is 37146.  Additionally, a process is scheduled to
 poll the REPL server upon every tick of the game loop."
   (let ((server (spawn-coop-repl-server port)))
-    (schedule-each game-agenda
-                   (lambda ()
-                     (poll-coop-repl-server server)))))
+    (schedule-each
+     (lambda ()
+       (poll-coop-repl-server server)))))
diff --git a/2d/signal.scm b/2d/signal.scm
index 58cb0a4..efbb103 100644
--- a/2d/signal.scm
+++ b/2d/signal.scm
@@ -260,33 +260,33 @@ SIGNAL.  This signal is a convenient way to sneak a procedure that has
 a side-effect into a signal chain."
   (signal-map (lambda (x) (proc x) x) signal))
 
-(define (signal-sample agenda delay signal)
+(define (signal-sample delay signal)
   "Create a new signal that emits the value contained within SIGNAL
-every DELAY ticks of AGENDA."
+every DELAY ticks of the current agenda."
   (let ((sampler (%make-signal (signal-ref signal) #f '())))
     (define (tick)
       (%signal-set! sampler (signal-ref signal)))
-    (schedule-interval agenda tick delay)
+    (schedule-interval tick delay)
     (make-signal-box sampler)))
 
-(define (signal-delay agenda delay signal)
+(define (signal-delay delay signal)
   "Create a new signal that delays propagation of SIGNAL by DELAY
-ticks of AGENDA."
+ticks of the current agenda."
   (make-boxed-signal (signal-ref signal)
                      (lambda (self value)
-                       (schedule agenda
-                                 (lambda ()
-                                   (%signal-set! self value))
-                                 delay))
+                       (schedule
+                        (lambda ()
+                          (%signal-set! self value))
+                        delay))
                      (list signal)))
 
-(define (signal-throttle agenda delay signal)
+(define (signal-throttle delay signal)
   "Return a new signal that propagates SIGNAL at most once every DELAY
-ticks of AGENDA."
+ticks of the current agenda."
   (make-boxed-signal (signal-ref signal)
-                     (let ((last-time (agenda-time agenda)))
+                     (let ((last-time (agenda-time)))
                        (lambda (self value)
-                         (when (>= (- (agenda-time agenda) last-time) delay)
+                         (when (>= (- (agenda-time) last-time) delay)
                            (%signal-set! self value)
-                           (set! last-time (agenda-time agenda)))))
+                           (set! last-time (agenda-time)))))
                      (list signal)))
diff --git a/2d/sprite.scm b/2d/sprite.scm
index 3b74fdb..c050a39 100644
--- a/2d/sprite.scm
+++ b/2d/sprite.scm
@@ -32,7 +32,6 @@
   #:use-module (2d animation)
   #:use-module (2d color)
   #:use-module (2d config)
-  #:use-module (2d game)
   #:use-module (2d helpers)
   #:use-module (2d math)
   #:use-module (2d shader)
@@ -175,8 +174,7 @@ currently bound."
                              1))))
 
 ;; A hash table for all of the animated sprites that have been drawn
-;; since the last game update.  It is cleared after every game-agenda
-;; tick.
+;; since the last game update.  It is cleared after every agenda tick.
 (define animated-sprites (make-hash-table))
 
 (define (register-animated-sprite-maybe sprite)
@@ -191,4 +189,4 @@ currently bound."
   (hash-clear! animated-sprites))
 
 ;; Update animated sprites upon every update.
-(schedule-each game-agenda update-animated-sprites!)
+(schedule-each update-animated-sprites!)
diff --git a/README.org b/README.org
index d54895a..bbd26e0 100644
--- a/README.org
+++ b/README.org
@@ -152,7 +152,7 @@
     exists a =wait= procedure to pause a coroutine and schedule it to
     be resumed later.
 
-    Using a coroutine and an agenda, the NPC script can be rewritten
+    Using a coroutine and the agenda, the NPC script can be rewritten
     such that it does not halt further program execution.
 
     #+BEGIN_SRC scheme
@@ -163,19 +163,18 @@
       (coroutine
        (while #t
          (walk 'up)
-         (wait game-agenda 60)
+         (wait 60)
          (walk 'down)
-         (wait game-agenda 60)))
+         (wait 60)))
 
     #+END_SRC
 
     =coroutine= is a useful macro that evaluates a block of code as a
     coroutine.  =wait= aborts the procedure and schedules the
-    continuation inside of an agenda.  =game-agenda= is the main
-    agenda that is ticked at each iteration of the game update loop.
-    In this example, the script is paused for 1 second after each
-    step.  Since guile-2d enforces a fixed timestep and updates 60
-    times per second by default, 60 ticks is equivalent to 1 second.
+    continuation inside of the agenda.  In this example, the script is
+    paused for 1 second after each step.  Since guile-2d enforces a
+    fixed timestep and updates 60 times per second by default, 60
+    ticks is equivalent to 1 second.
 
     You can also use the agenda to schedule the evaluation of any
     thunk even if it isn't a coroutine.
@@ -184,7 +183,7 @@
       (define (hello)
         (display "Hello, world!  Sorry I'm late!\n"))
 
-      (schedule game-agenda hello 600)
+      (schedule hello 600)
     #+END_SRC
 
     =schedule= accepts a thunk (a procedure that takes no arguments)
@@ -220,7 +219,7 @@
         (signal-fold v+ (vector2 320 240)
                      (signal-map (lambda (v)
                                    (vscale v 4))
-                                 (signal-sample game-agenda 1 key-arrows))))
+                                 (signal-sample 1 key-arrows))))
     #+END_SRC
 
     This signal describes a relationship between the arrow keys on the
diff --git a/examples/common.scm b/examples/common.scm
index 0acb6c2..62ddd14 100644
--- a/examples/common.scm
+++ b/examples/common.scm
@@ -33,9 +33,9 @@
 
 (add-hook! window-close-hook stop-game-loop)
 
-(schedule-interval game-agenda
-                   (lambda ()
-                     (format #t "FPS: ~d\n" (signal-ref fps)))
-                   60)
+(schedule-interval
+ (lambda ()
+   (format #t "FPS: ~d\n" (signal-ref fps)))
+ 60)
 
 (start-2d-repl)
diff --git a/examples/coroutine.scm b/examples/coroutine.scm
index 98dec16..7b4a1e6 100644
--- a/examples/coroutine.scm
+++ b/examples/coroutine.scm
@@ -38,9 +38,9 @@
     sprite
     (vector2 (random window-width)
              (random window-height)))
-   (wait game-agenda 15)
+   (wait 15)
    (set-sprite-rotation! sprite (random 360))
-   (wait game-agenda 15)))
+   (wait 15)))
 
 (add-hook! draw-hook (lambda (dt alpha) (draw-sprite sprite)))
 
diff --git a/examples/font.scm b/examples/font.scm
index 304070f..8bcd90d 100644
--- a/examples/font.scm
+++ b/examples/font.scm
@@ -44,7 +44,7 @@
   (signal-map (lambda (p)
                 (let ((text (format #f "Mouse: (~d, ~d)" (vx p) (vy p))))
                   (make-label font text (vector2 0 20))))
-              (signal-throttle game-agenda 5 mouse-position)))
+              (signal-throttle 5 mouse-position)))
 
 (add-hook! draw-hook (lambda (dt alpha)
                        (draw-label label)
diff --git a/examples/particles.scm b/examples/particles.scm
index d811eb7..4269b99 100644
--- a/examples/particles.scm
+++ b/examples/particles.scm
@@ -76,7 +76,7 @@
 (define (update)
   (for-each update-particle! particles))
 
-(schedule-each game-agenda update)
+(schedule-each update)
 (add-hook! draw-hook draw)
 
 (with-window (make-window #:title "Particles"