Сортировка сл-ем на сопрограммах Concurrent_mergesort

//сортировка слиянием
package main
import "fmt"

var i, n, x int
var arr []int

func mergesort (first int, last int, ch chan int) {

    if first >= last {
        ch <- arr[first]
        close(ch)
    } else {
        var a, b, t_a, t_b, mid int = 0, 0, 0, 0, (first + last) / 2
        var chan1, chan2 = make(chan int), make(chan int)

        go mergesort(first, mid, chan1)
        go mergesort(mid + 1, last, chan2)

        a, ok1 := <-chan1
        b, ok2 := <-chan2

        for (ok1 || ok2) && (p != 3) {
            if ok1 && ok2 {
                if a < 0 { t_a = -a } else { t_a = a }
                if b < 0 { t_b = -b } else { t_b = b }
                if t_a > t_b {
                    ch <- b
                    b, ok2 = <-chan2
                } else {
                    ch <- a
                    a, ok1 = <-chan1
                }
            }
                        if ok1 && !ok2 {
                ch <- a
                a, ok1 = <-chan1
            }
            if ok2 && !ok1 {
                ch <- b
                b, ok2 = <-chan2
            }
        }
        close(ch)
    }
}

func main() {
    input.Scanf("%d", &n)
    arr = make([]int, n)
    for i = 0; i < n; i++ { input.Scanf("%d", &arr[i]) }
    if 1 == n {
        fmt.Printf("%d", arr[0])
        return
    }
        ch := make(chan int)
    go mergesort(0, n - 1, ch)

    for i = 0; i < n; i++ { fmt.Printf("%d ", <-ch) }
}