Implement Go's canonical pipeline pattern with cancellation from the Go blog.

The Go blog defines three-stage pipelines: a generator that produces values, one or more transformation stages, and a consumer — all connected by directional channels, with cancellation via context.

// Stage 1: Generator
func generate(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
}

// Stage 2: Transform
func square(ctx context.Context, in <-chan int) <-chan int {
    out := make(chan int)
    go func() {
        defer close(out)
        for v := range in {
            select {
            case out <- v * v:
            case <-ctx.Done(): return
            }
        }
    }()
    return out
}

// Stage 3: Filter
func filterAbove(ctx context.Context, in <-chan int, min int) <-chan int {
    out := make(chan int)
    go func() {
        defer close(out)
        for v := range in {
            if v <= min { continue }
            select {
            case out <- v:
            case <-ctx.Done(): return
            }
        }
    }()
    return out
}

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

    nums    := generate(ctx, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    squares := square(ctx, nums)
    results := filterAbove(ctx, squares, 25)

    for i := 0; i < 3; i++ { fmt.Println(<-results) }
    cancel() // stops all upstream stages cleanly
}

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