Function reduce

The reduce() method executes a user-supplied "reducer" callback function on each element of the iterator, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the array is a single value, so the ouput iterator will only produce 1 result before finishing.

Example

   pipe(
     itr8FromArray([ 1, 2, 3, 4 ]),
     reduce((acc, cur) => acc + cur, 0),
   );
   // => [ 10 ]

The reduce function can be an asynchronous function (in which case the resulting iterator will be asynchronous regardless of the input iterator)!