Output the most recent input received.
<p>At each tick of the clock, this actor outputs the most recently received
non-absent input. If no input has been received, then the output is absent.
This implements the Lustre "current" operator.
<p>P. Caspi, D. Pilaud, N. Halbwachs, and J. A. Plaice, "LUSTRE: A
Declarative Language for Programming Synchronous Systems,"
Conference Record of the 14th Annual ACM Symp. on Principles of
Programming Languages, Munich, Germany, January, 1987.
Paul Whitaker, Christopher Hylands, Edward A. Lee
$Id: Current.java 70398 2014-10-22 23:44:32Z cxh $
Ptolemy II 4.1
Yellow (cxh)
Red (cxh) Should support multiports