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CSS

              
                
              
            
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JS

              
                // compose helper higher order function
var compose = (...fns) => x => fns.reduceRight((y, f) => f(y), x);

// resolver helper that call function on actual value
var resolve = (value, fn) => {
    if (value instanceof Promise) {
         return value.then(fn);
    } else {
        return fn(value);
    }
};

// map reducer
var map = f => reducing => (result, input) => {
    return reducing(result, resolve(input, f));
};

// filtering reducer
var filter =  predicate => reducing => (result, input) => {
  const ret = cond => cond ? reducing(result, input) : result;
  return resolve(resolve(input, predicate), ret);
}

// async aware conector function helper
var connector = fn => (accumulator, element) => {
   return resolve(accumulator, (acc) => {
      return resolve(element, (e) => fn(acc, e));
   });
}

var concat = connector((acc, item) => acc.concat(item));
var sum = connector((a, b) => a + b);

// standard transducer
var transducer = compose(map(x => x + 1), filter(x => x % 2 === 0));

// async code
(async function() {
    var promises = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].map(n => Promise.resolve(n));

    var result = await promises.reduce(transducer(concat), Promise.resolve([]));
    console.log(result);
    var result = await promises.reduce(transducer(sum), Promise.resolve(0));
    console.log(result);
})();

// sync code
var result = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    .reduce(transducer(concat), []);
console.log(result);

var result = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    .reduce(transducer(sum), 0);
console.log(result);
              
            
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