Add signal-ref-maybe procedure.

* 2d/signals.scm (signal-ref-maybe): New procedure.

1 files changed, 9 insertions, 1 deletions

diff --git a/2d/signals.scm b/2d/signals.scm
index 4a455c2..28d2c6f 100644
--- a/2d/signals.scm
+++ b/2d/signals.scm
@@ -29,6 +29,7 @@
             signal?
             make-signal
             signal-ref
+            signal-ref-maybe
             signal-transformer
             signal-listeners
             signal-connect!
@@ -66,12 +67,19 @@
                       (init #f) (connectors '()))
   "Create a new signal with initial value INIT that uses the given
 TRANSFORMER procedure to process incoming values from another
-signal. Additionally, the signal will be connected to all of the
+signal.  Additionally, the signal will be connected to all of the
 signals in the list CONNECTORS."
   (let ((signal (%make-signal init transformer '())))
     (for-each (cut signal-connect! <> signal) connectors)
     signal))
 
+(define (signal-ref-maybe object)
+  "Dereferences OBJECT if it is a signal and returns OBJECT
+otherwise."
+  (if (signal? object)
+      (signal-ref object)
+      object))
+
 (define (%signal-transform signal value from)
   "Call the transform procedure for SIGNAL with VALUE."
   ((signal-transformer signal) value (signal-ref signal) from))