From f36ee4549eca5a6754289befdda9bf9cc93a0ee9 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Wed, 10 Feb 2016 21:58:41 -0500
Subject: signal: Add signal-if.

* sly/signal.scm (signal-if): New syntax.
---
 sly/signal.scm | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sly/signal.scm b/sly/signal.scm
index 5bd9a29..42cce40 100644
--- a/sly/signal.scm
+++ b/sly/signal.scm
@@ -48,6 +48,7 @@
             signal-drop
             signal-drop-repeats
             signal-switch
+            signal-if
             signal-constant
             signal-count
             signal-tap
@@ -341,6 +342,9 @@ signal PRED is true, or the value of the signal OFF otherwise."
                        (%signal-set! self (current-value)))
                      (list predicate)))
 
+(define-syntax-rule (signal-if predicate consequent alternate)
+  (signal-map (lambda (true?) (if true? consequent alternate)) predicate))
+
 (define (signal-constant constant signal)
   "Create a new signal whose value is always CONSTANT no matter the
 value of SIGNAL."
-- 
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