ListT instance smells funny

[treeowl]

ListT from transformers isn't really a monad transformer, so it seems most unlikely to be a valid Bound instance with the default definition.

[phadej]

So what's it will mean to have

| Weird (ListT Exp a)
| Weird (Exp [a])

Will have a AST node type "of type" a, yet having commuting multiple values (potentially none). I don't know what's that can be useful for, but I don't see it's unlawful either.

[treeowl]

I have no idea.