Go.vapi

[CCode (cheader_filename = "hello.h")]
namespace Go {
    [CCode (cname = "hello")]
    extern void hello();
}

hello.go

package main

import (
    "fmt"
    "C"
)

//export hello
func hello() {
    fmt.Println("hello, world from Go")
}

func main() {}

hello.vala

public static int main(string[] args) {

    stdout.printf("hello, world from Vala\n");
    Go.hello();

    return 0;
}