Nice little DAG walking in Go language from http://golang.org/src/cmd/go/pkg.go

gistfile1.go

// packageList returns the list of packages in the dag rooted at roots
// as visited in a depth-first post-order traversal.
func packageList(roots []*Package) []*Package {
    
	seen := map[*Package]bool{}
	all := []*Package{}
	var walk func(*Package)
	walk = func(p *Package) {
		if seen[p] {
			return
		}
		seen[p] = true
		for _, p1 := range p.imports {
			walk(p1)
		}
		all = append(all, p)
	}
	for _, root := range roots {
		walk(root)
	}
	return all
}