Pipeline

package main

import (
	"context"
	"fmt"
)

func gen(ctx context.Context, nums ...int) <-chan int {
	out := make(chan int)
	go func() {
		defer close(out)
		for _, n := range nums {
			select {
			case out <- n:
			case <-ctx.Done():
				return
			}
		}
	}()
	return out
}

func square(ctx context.Context, in <-chan int) <-chan int {
	out := make(chan int)
	go func() {
		defer close(out)
		for n := range in {
			select {
			case out <- n * n:
			case <-ctx.Done():
				return
			}
		}
	}()
	return out
}

func filterEven(ctx context.Context, in <-chan int) <-chan int {
	out := make(chan int)
	go func() {
		defer close(out)
		for n := range in {
			if n%2 == 0 {
				select {
				case out <- n:
				case <-ctx.Done():
					return
				}
			}
		}
	}()
	return out
}

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	nums := gen(ctx, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
	squared := square(ctx, nums)
	evens := filterEven(ctx, squared)

	for val := range evens {
		fmt.Println(val)
	}
}