digraph block {
    N0[label="entry"];
    N1[label="exit"];
    N2[label="expr 4"];
    N3[label="local _x"];
    N4[label="block { let _x = 4; }"];
    N0 -> N2;
    N2 -> N3;
    N3 -> N4;
    N4 -> N1;
}