This is also the natural solution when you're using Datalog to compute with the AST: Datalog operates on relations/tables, so associating types to AST nodes can be accomplished using a table with two columns: One for the ID representing an AST node, and one for the type associated to the AST node. I've recently written about this approach in the series starting here: https://www.mbid.me/posts/type-checking-with-eqlog-parsing/
