digraph G{
    // Inheritance links between superclasses
    Expression -> Action [arrowhead="empty"];
    Statement -> Action [arrowhead="empty"];
    Action -> Any [arrowhead="empty"];

    // Links on superclasses
    Statement -> Statement [label="next"];

    // Inheritance hierarchy
    If -> Statement [arrowhead="empty"];
    While -> Statement [arrowhead="empty"];
    Assign -> Statement [arrowhead="empty"];
    Call -> Statement [arrowhead="empty"];
    Call -> Expression [arrowhead="empty"];
    Break -> Statement [arrowhead="empty"];
    Continue -> Statement [arrowhead="empty"];
    Return -> Statement [arrowhead="empty"];
    Resolve -> Statement [arrowhead="empty"];
    Resolve -> Lvalue [arrowhead="empty"];
    Access -> Expression [arrowhead="empty"];
    Constant -> Expression [arrowhead="empty"];
    Constant -> Lvalue [arrowhead="empty"];
    Input -> Expression [arrowhead="empty"];
    Output -> Statement [arrowhead="empty"];
    Declare -> Statement [arrowhead="empty"];
    Global -> Statement [arrowhead="empty"];

    // Actual types
    // If
    If -> Expression [label="cond"];
    If -> Statement [label="true"];
    If -> Statement [label="false"];

    // While
    While -> Expression [label="cond"];
    While -> Statement [label="body"];

    // Assign
    Assign -> Lvalue [label="var"];
    Assign -> Expression [label="value"];

    // Call
    Call -> Expression [label="func"];
    Call -> Param [label="params"];
    Call -> Param [label="last_param"];

    // Break
    Break -> While [label="while"];
    
    // Continue
    Continue -> While [label="while"];

    // Return
    Return -> Expression [label="value"];

    // Resolve
    Resolve -> Any [label="var"];

    // Access
    Access -> Lvalue [label="var"];

    // Constant
    Constant -> Any [label="node"];

    // Input

    // Output
    Output -> Any [label="value"];

    // Declare

    // Global
    Global -> String [label="var"];

    // Param
    Param -> String [label="name"];
    Param -> Expression [label="value"];
    Param -> Param [label="next_param"];

    // Function definition
    Funcdef -> Statement [label="body"];
}