Reducers #

To support generating aggregated values ,like the sum,mean or max of a set of values, go-optics includes the Reducer interface. This enables the Reduce combinator to focus the aggregate value.

A Reducer is built from 3 components.

1. An empty value to begin the reduction from e.g. for Sum this would be 0.
2. A reduce function that takes the current state and a value and returns the new state. e.g. for Mean this might be the current sum and the number of reduced elements.
3. An end function that takes the final state and returns the final value. e.g. For Mean this would calculate the final Mean value. The Reduce combinator can then be used to apply this Reducer to the foci of an optic.

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10

	data := []int{1, 2, 3, 4}

	result, ok := MustGetFirst(
		Reduce(
			TraverseSlice[int](),
			Sum[int](),
		),
		data,
	)
	fmt.Println(result, ok)

If the optic focuses no values then ok will be false. In this example result is the value 10.

Reducers can be created from compatible ReturnOne optics using the AsReducer constructor.

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	sum := AsReducer(
		0,            //Initial value
		AddT2[int](), //Reduction operation
	)

0 is the empty value. AddT2 is a built in operation that takes a tuple of 2 ints and returns their sum. This is used as the reduce function.

The following Reducers are provided