a tree, in go

tree.go

package main

import (
	"fmt"
	"io"
	"os"
)

type Tree struct {
	Children []*Tree
	Value    interface{}
}

func NewTree(v interface{}) *Tree {
	return &Tree{
		Children: []*Tree{},
		Value:    v,
	}
}

func (t *Tree) String() string {
	return fmt.Sprint(t.Value)
}

func (t *Tree) PrettyPrint(w io.Writer, prefix string) {
	var inner func(int, *Tree)
	inner = func(depth int, child *Tree) {
		for i := 0; i < depth; i++ {
			io.WriteString(w, prefix)
		}
		io.WriteString(w, child.String()+"\n") // you should really observe the return value here.
		for _, grandchild := range child.Children {
			inner(depth+1, grandchild)
		}
	}
	inner(0, t)
}

func (t *Tree) AddChild(child interface{}) {
	switch c := child.(type) {
	case *Tree:
		t.Children = append(t.Children, c)
	default:
		t.Children = append(t.Children, NewTree(c))
	}
}

func main() {
	root := NewTree("this is the root")
	root.AddChild("this is a child")
	root.AddChild("this is also a child")
	root.AddChild("again, another child")
	child := NewTree("now this one will have some children")
	child.AddChild(5)
	child.AddChild(1.3)
	child.AddChild("the types can be mixed.")
	grandchild := NewTree("etc, here's a grandhcild node.")
	grandchild.AddChild("this one's a great grandchild")
	grandchild.AddChild("semantic satiation means that the word child doesn't mean anything any more")
	child.AddChild(grandchild)
	child.AddChild("that's just fine.  Maybe you don't want to do it, though")
	root.AddChild(child)
	root.AddChild("you see?")
	root.AddChild("not so terrible.")
	root.PrettyPrint(os.Stdout, "\t")

	fmt.Print("\n\n\n\n")
	child.PrettyPrint(os.Stdout, " - ")
}