go version go1.6.2 linux/amd64

GOARCH="amd64"
GOBIN="/home/songgao/gopath/bin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/songgao/gopath"
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GO15VENDOREXPERIMENT="1"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="g++"
CGO_ENABLED="1"

songgao at Song-ThinkPad in /tmp 
$ cat main.go
package main

func main() {
    var a int
    a = 2
}

songgao at Song-ThinkPad in /tmp 
$ go run main.go
# command-line-arguments
./main.go:4: a declared and not used

songgao at Song-ThinkPad in /tmp 
$ vim main.go

songgao at Song-ThinkPad in /tmp 
$ cat main.go
package main

func main() {
    var a int
    func() {
        a = 2
    }()
}

songgao at Song-ThinkPad in /tmp 
$ go run main.go

songgao at Song-ThinkPad in /tmp 
$ echo $?
0