lazy.go

package main

import "fmt"

type EvalFunc func(interface{}) (interface{}, interface{})

func BuildLazyEvaluator(evalFunc EvalFunc, initState interface{}) func() interface{} {
	retValChan := make(chan interface{})

	loopFunc := func() {
		var actState interface{} = initState
		var retVal interface{}

		for {
			retVal, actState = evalFunc(actState)
			retValChan <- retVal
		}
	}

	retFunc := func() interface{} {
		return <-retValChan
	}

	go loopFunc()

	return retFunc
}

func BuildLazyIntEvaluator(evalFunc EvalFunc, initState interface{}) func() int {
	ef := BuildLazyEvaluator(evalFunc, initState)
	return func() int {
		return ef().(int)
	}
}

func main() {
	evenFunc := func(state interface{}) (interface{}, interface{}) {
		now := state.(int)
		next := now + 2

		return now, next
	}

	even := BuildLazyIntEvaluator(evenFunc, 0)

	for i := 0; i < 10; i++ {
		fmt.Printf("Even %v: %v\n", i, even())
	}

	fibFunc := func(state interface{}) (interface{}, interface{}) {
		now := state.([]int)
		v1 := now[0]
		v2 := now[1]
		next := []int{v2, v1 + v2}
		return v1, next
	}

	fib := BuildLazyIntEvaluator(fibFunc, []int{0, 1})

	for i := 0; i < 10; i++ {
		fmt.Printf("Fib %v: %v\n", i, fib())
	}
}

Goでlazy Evaluation
参考: https://sites.google.com/site/tidelandbiz/articles/coding-in-go/build-functions-for-lazy-evaluation