Go to Crystal: Concurrency Tour #2 (https://tour.golang.org/concurrency/2)

concurrency_2.cr

def sum(s : Array(Int32), c : Channel(Int32))
  c.send s.reduce(0) { |sum, v| sum + v }
end

def main
  s = [7, 2, 8, -9, 4, 0]
  c = Channel(Int32).new
  spawn {
    sum(s[0..((s.size / 2) - 1)], c)
  }
  spawn {
    sum(s[(s.size / 2)..-1], c)
  }
  x, y = c.receive, c.receive

  puts "x, y = #{x}, #{y}"
end

main

concurrency_2.go

package main

import "fmt"

func sum(s []int, c chan int) {
	sum := 0
	for _, v := range s {
		sum += v
	}
	c <- sum // send sum to c
}

func main() {
	s := []int{7, 2, 8, -9, 4, 0}

	c := make(chan int)
	go sum(s[:len(s)/2], c)
	go sum(s[len(s)/2:], c)
	x, y := <-c, <-c // receive from c

	fmt.Println(x, y, x+y)
}

@akitaonrails Nice! But I'd say this is more idiomatic Crystal (no need for main, can use spawn without a block, like in Go):

def sum(s : Array(Int32), c : Channel(Int32))
  c.send s.sum
end

s = [7, 2, 8, -9, 4, 0]
c = Channel(Int32).new
spawn sum(s[0..((s.size / 2) - 1)], c)
spawn sum(s[(s.size / 2)..-1], c)
x, y = c.receive, c.receive

puts "x, y = #{x}, #{y}"

Or maybe even this (type annotations are not required in arguments):

def sum(values, channel)
  channel.send values.sum
end

s = [7, 2, 8, -9, 4, 0]
c = Channel(Int32).new
spawn sum(s[0..((s.size / 2) - 1)], c)
spawn sum(s[(s.size / 2)..-1], c)
x, y = c.receive, c.receive

puts "x, y = #{x}, #{y}"

Great, I agree, I was just doing a 1 to 1 translation just to show the difference but your version is definitely better.