Transducers

transducers.js

const dragons = [
  { name: 'fluffykins', size: 1 },
  { name: 'wargle', size: 3 }
]
for(let i=0; i<500; i++) {
  dragons.push({ name: 'fluffykins', size: Math.random()*10 })
}

const getDragonTitle = dragon => {
  if (dragon.size > 1) {
    return dragon.name + ' the great'
  }
  return dragon.name + ' the tiny'
}
const arrayReducer = (target, cur) => 
  target.concat(cur)
''
const stringReducer = (target, cur) =>
  target + cur 

// map = (transform) => (reducer) => ...
function makeReducerFromTransform(reducer, transform) {
  return (target, cur) => {
    const processed = transform(cur)
    return reducer(target, processed)
  }
}
function tMap(transform) {
  return function transduce (reducer) {
    return (target, cur) => {
      const processed = transform(cur)
      return reducer(target, processed)
    }
  }
}
function tFilter(predicate) {
  return function transduce (reducer) {
    return (target, cur) => {
      if(predicate(cur))
        return reducer(target, cur)
      return target
    }
  }
}

// getDragonTitle = map(dragon => { }) //
// const getName = map(item => item.name)
const toUpperCase = name => name.toUpperCase()
const isGreat = dragon => {
  console.log('')
  return dragon => dragon.size > 1
}
const dragonTitleTransducer = tMap(getDragonTitle)
const upperCaseTransducer = tMap(toUpperCase)
const isGreatDragonTransducer = tFilter(isGreat)

const dumbCompose = (...fns) => val => {
  let lastResult = null
  for (const fn of fns) {
    lastResult = fn(lastResult || val)
  }
  return lastResult
}

const optimizedCompose = (...fs) => fs.reduceRight((g, f) => x => g(f(x)));

dragons.reduce(
  dumbCompose(
    upperCaseTransducer,
    dragonTitleTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
    isGreatDragonTransducer,
  )(arrayReducer), []
) //?.

dragons
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .filter(isGreat)
    .map(getDragonTitle)
    .map(toUpperCase) //?.

dragons.reduce(
  isGreatDragonTransducer(
    dragonTitleTransducer(
      upperCaseTransducer(arrayReducer))), []) //?.







/*
dragons.map(dragon => {
  if (dragon.size > 1) {
    return dragon.name + ' the great'
  }
  return dragon.name + ' the tiny'
})
*/
//dragons //?
/*
function map2(arr, transform) {
  return arr.reduce(abstractAbstracterson(transform)(arrayReducer), [])
}

function map1(arr, transform) {
  return arr.reduce((target, cur) => {
    const processed = transform(cur)
    return target.concat(processed)
  }, [])
}
map1(dragons, getDragonTitle) //?
map2(dragons, getDragonTitle) 
*/