transduction-block08.js

const mapReduce = mapperFn => combinerFn => (accumulator, currentValue) => {
  return combinerFn(accumulator, mapperFn(currentValue));
};

const filterReduce = predicateFn => combinerFn => (accumulator, currentValue) => {
  if (predicateFn(currentValue)) {
    return combinerFn(accumulator, currentValue);
  }
  return accumulator;
};

const combinerConcat = (accumulator, currentValue) => {
  accumulator.push(currentValue);
  return accumulator;
};

const transducer = pipe(
  mapReduce(addBy1),
  mapReduce(multiplyBy2),
  filterReduce(getItemsBelow10)
);

const mapTransducer = mapReduce(addBy1)
// mapTransducer:: combinerFn -> (accumulator, currentValue) -> result

const filterTransducer = filterReduce(getItemsBelow10)
// filterTransducer:: combinerFn -> (accumulator, currentValue) -> result


const mapTransducerWithCombiner = mapReduce(addBy1)(combinerConcat)
// mapTransducerWithCombiner:: (accumulator, currentValue) -> result

const filterTransducerWithCombiner = filterReduce(getItemsBelow10)(combinerConcat)
// filterTransducerWithCombiner:: (accumulator, currentValue) -> result

// Execution of `mapTransducerWithCombiner` and `filterTransducerWithCombiner` in the `pipe`

const transducerWithCombiner = pipe(
  mapReduce(addBy1)(combinerConcat), // returns a result
  filterReduce(getItemsBelow10)(combinerConcat), // expects a (accumulator, currentValue) -> result 
);

// BREAK! Incorrect function signature