package node type Nullable struct { name string expr Node } func (n Nullable) Name() string { return "Nullable" } func NewNullable(expression Node) Node { return Nullable{ "Nullable", expression, } } func (n Nullable) Walk(v Visitor) { if v.EnterNode(n) == false { return } if n.expr != nil { vv := v.GetChildrenVisitor("expr") n.expr.Walk(vv) } v.LeaveNode(n) }