Add hook->signal procedure.

* 2d/signal.scm (hook->signal): New procedure.

1 files changed, 11 insertions, 0 deletions

diff --git a/2d/signal.scm b/2d/signal.scm
index 53f676a..4d6fe3f 100644
--- a/2d/signal.scm
+++ b/2d/signal.scm
@@ -30,6 +30,7 @@
             signal-box?
             make-signal
             define-signal
+            hook->signal
             signal-ref
             signal-ref-maybe
             signal-set!
@@ -148,6 +149,16 @@ be spliced into the new signal."
 ;;; Higher Order Signals
 ;;;
 
+(define (hook->signal hook init proc)
+  "Return a new signal whose initial value is INIT and has future
+values calculated by applying PROC to the arguments sent when HOOK is
+run."
+  (let ((signal (make-signal init)))
+    (add-hook! hook
+               (lambda args
+                 (signal-set! signal (apply proc args))))
+    signal))
+
 (define (signal-merge signal1 signal2 . rest)
   "Create a new signal whose value is the that of the most recently
 changed signal in SIGNALs.  The initial value is that of the first