Add optional start and step parameters to signal-count.

* sly/signal.scm (signal-count): Add start and step parameters.

1 files changed, 5 insertions, 4 deletions

diff --git a/sly/signal.scm b/sly/signal.scm
index aab18b8..3988812 100644
--- a/sly/signal.scm
+++ b/sly/signal.scm
@@ -276,10 +276,11 @@ signal PRED is true, or the value of the signal OFF otherwise."
 value of SIGNAL."
   (signal-map (lambda (value) constant) signal))
 
-(define (signal-count signal)
-  "Create a new signal that increments a counter every time a new
-value from SIGNAL is received."
-  (signal-fold + 0 (signal-constant 1 signal)))
+(define* (signal-count signal #:optional (start 0) (step 1))
+  "Create a new signal that increments a counter by STEP every time a
+new value from SIGNAL is received, with an initial value of START.  By
+default, START is 0 and STEP is 1."
+  (signal-fold + start (signal-constant step signal)))
 
 (define (signal-tap proc signal)
   "Create a new signal that applies PROC when a new value is received