/**
 * A simple FIR actor. It assumes the presence of the following functions:
 *
 *  [T] zero : [--> T]
 *  [T] plus : [T, T --> T]
 *  [T] multiply : [T, T --> T]
 *  [T1, T2] collect : [T1, [T1, T2 --> T1], List[T2] --> T1]
 *  [T1, T2, T3] combine : [[T1, T2 --> T3], List[T1], List[T2] --> List[T3]]
 *
 * @author JWJ
 */


actor SimpleFIR [T < Group[T]]
    (List[T] taps)	// the taps are the coefficients, starting
                        // with the one for the most recent data item 

    T input ==> T output :

    List[T] data := [zero() : for Integer i in Integers(1, #taps)];

    action [a] ==> [b] 
    var
        T b := collect(zero(), plus, combine(multiply, taps, data))
    do
        data := [a] + [data[i] : for Integer i in Integers(0, #taps-2)];
    endaction
endactor