From 5e8aab990b355ed51b409fb1916afd6b8848c8b8 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Thu, 27 Apr 2017 22:26:06 -0400
Subject: scripting: agenda: Add 'every' scheduling option.

* chickadee/scripting/agenda.scm (schedule-every): New procedure.
(every): New syntax.
* doc/api.texi (Agendas): Document it.
---
 chickadee/scripting/agenda.scm | 24 +++++++++++++++++++++++-
 doc/api.texi                   | 12 ++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/chickadee/scripting/agenda.scm b/chickadee/scripting/agenda.scm
index c815afa..f16dc45 100644
--- a/chickadee/scripting/agenda.scm
+++ b/chickadee/scripting/agenda.scm
@@ -28,8 +28,10 @@
             clear-agenda
             schedule-at
             schedule-after
+            schedule-every
             at
-            after))
+            after
+            every))
 
 (define-record-type <agenda>
   (%make-agenda time queue)
@@ -93,8 +95,28 @@
   "Schedule THUNK to be run after DELAY."
   (schedule (current-agenda) (+ (agenda-time) delay) thunk))
 
+(define* (schedule-every interval thunk #:optional n)
+  "Schedule THUNK to run every INTERVAL amount of time.  Repeat this N
+times, or indefinitely if not specified."
+  (schedule-after interval
+                  (lambda ()
+                    (cond
+                     ((not n)
+                      (thunk)
+                      (schedule-every interval thunk))
+                     ((> n 0)
+                      (thunk)
+                      (schedule-every interval thunk (- n 1)))))))
+
 (define-syntax-rule (at time body ...)
   (schedule-at time (lambda () body ...)))
 
 (define-syntax-rule (after delay body ...)
   (schedule-after delay (lambda () body ...)))
+
+(define-syntax every
+  (syntax-rules ()
+    ((_ (interval n) body ...)
+     (schedule-every interval (lambda () body ...) n))
+    ((_ interval body ...)
+     (schedule-every interval (lambda () body ...)))))
diff --git a/doc/api.texi b/doc/api.texi
index e1f6acc..1a56039 100644
--- a/doc/api.texi
+++ b/doc/api.texi
@@ -955,6 +955,12 @@ Schedule @var{thunk}, a procedure of zero arguments, to be run after
 @var{delay}.
 @end deffn
 
+@deffn {Scheme Procedure} schedule-every @var{interval} @var{thunk} [@var{n}]
+Schedule @var{thunk}, a procedure of zero arguments, to be run every
+@var{interval} amount of time.  Repeat this @var{n} times, or
+indefinitely if not specified.
+@end deffn
+
 @deffn {Scheme Syntax} at @var{time} @var{body} @dots{}
 Schedule @var{body} to be evaluated at @var{time}.
 @end deffn
@@ -963,6 +969,12 @@ Schedule @var{body} to be evaluated at @var{time}.
 Schedule @var{body} to be evaluated after @var{delay}.
 @end deffn
 
+@deffn {Scheme Syntax} every @var{interval} @var{body} @dots{}
+@deffnx {Scheme Syntax} every (@var{interval} @var{n}) @var{body} @dots{}
+Schedule @var{body} to be evaluated every @var{interval} amount of
+time.  Repeat this @var{n} times, or indefinitely if not specified.
+@end deffn
+
 @node Coroutines
 @subsection Coroutines
 
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