Returns a single item by iterating through the list, successively calling the iterator function and passing it an accumulator value and the current value from the array, and then passing the result to the next call.

The iterator function receives two values: (acc, value). It may use R.reduced to shortcut the iteration.

The arguments' order of reduceRight's iterator function is (value, acc).

Note: R.reduce does not skip deleted or unassigned indices (sparse arrays), unlike the native Array.prototype.reduce method. For more details on this behavior, see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#Description

Dispatches to the reduce method of the third argument, if present. When doing so, it is up to the user to handle the R.reduced shortcuting, as this is not implemented by reduce.