kefir/src/one-source/transduce.js

Reactive Programming library for JavaScript inspired by Bacon.js and RxJS with focus on high performance and low memory usage

import {createStream, createProperty} from '../patterns/one-source'

function xformForObs(obs) {
  return {
    '@@transducer/step'(res, input) {
      obs._emitValue(input)
      return null
    },

    '@@transducer/result'() {
      obs._emitEnd()
      return null
    },
  }
}

const mixin = {
  _init({transducer}) {
    this._xform = transducer(xformForObs(this))
  },

  _free() {
    this._xform = null
  },

  _handleValue(x) {
    if (this._xform['@@transducer/step'](null, x) !== null) {
      this._xform['@@transducer/result'](null)
    }
  },

  _handleEnd() {
    this._xform['@@transducer/result'](null)
  },
}

const S = createStream('transduce', mixin)
const P = createProperty('transduce', mixin)

export default function transduce(obs, transducer) {
  return new (obs._ofSameType(S, P))(obs, {transducer})
}