Is it possible to implement scan as a transducer

Question

I notice that scan is missing from the various transducer libraries that I looked at (e.g transducers-js). Is it impossible to implement or am I missing something?

Answer 1

Actually I can answer my own question. I was trying to implement it in a functional way and I misunderstood how the transducer interface is used. Looking at the source code from transducers-js, they generally keep state in an object and I can implement scan the same way:

var Scan = function( agg, start, xf ){
    this.xf = xf;
    this.agg = agg;
    this.accum = start;
}
Scan.prototype.init = function(){
    return this.xf.init();
}
Scan.prototype.result = function(v) {
    return this.xf.result(v);
}
Scan.prototype.step = function( result, input ) {
    this.accum = this.agg( this.accum, input );
    return this.xf.step( result, this.accum );
}

var scan = function(agg, start) {
    return function (xf) {
        return new Scan(agg, start, xf);
    }
}