Without generics you'll need to use an alternative approach. As you said you can use interface{} everywhere. Another option is to create an interface that does what you need. Checkout "sort" for an example: http://golang.org/pkg/sort/#Interface.
Sure, I can `type Tree struct { Child []*Tree; Node NodeType }`, where `NodeType` is either `interface{}` (makes `Tree` reusable by sacrificing type safety) or some concrete type (sacrifices `Tree`'s reuse) but that's about how far I can progress. Also, I have to manually ensure that only one of Child or Node is set, but not both.
I just can't do anything like `data Tree a = Leaf a | Node [Tree a]` there.
(Edit: okay, my mind swayed a bit, that was trees, not graphs. I had different ideas on data structure to use, and my memories are a bit messy. Sorry about this. The problem should still hold, it applies to both trees and graphs, and I think many other data structures too.)
The 'one of Child or Node' isn't really an issue since you probably shouldn't expose the members of the struct (the tree should be accessed via methods). But I agree with your point about containers.
I think he already covered both, the second with "or I have to write my own separate implementation for every and each type of graph I'll use, without any significant way to reuse code".
