How do I create a transformer with state?

[shaunc]

I assume something like the following?

var MapWithState = function(f, xf) {
    return {
       "@@transducer/init": function() { 
           return {wraps: xf["@@transducer/init"](), mystate: {...}}; 
       },
       "@@transducer/result": function(result) { 
           return xf["@@transducer/result"](result.wraps); 
       },
       "@@transducer/step": function(result, input) {
           return xf["@@transducer/step"](result.wraps, f(result.mystate, input)); 
       }
    };
};
... Ie -- in result and step, I am guaranteed to be passed back whatever I created, and I guarantee that I pass back the wrapped state to the next transformer? ... However this protocol is supposed to work it should be documented....