Golang error checking closure

errs.go

func httpRequestHandler(w http.ResponseWriter, req *http.Request) {

    err := func () os.Error {

        if req.Method != "GET" {
            return os.NewError("expected GET")
        }

        if input := parseInput(req); input != "command" {
            return os.NewError("malformed command")
        }
    } ()

    if err != nil {
        w.WriteHeader(400)
        io.WriteString(w, err)
        return
    }

    doSomething() ...
...