Dear Araq, how do I create a programming language?

[Araq]

The visitor pattern hides the dispatching mechanism but you don't want to hide 
that, it's the foundation for pattern matching on the AST or graph data 
structure that you always need to do. Often it does the dispatching on the 
wrong granularity as it's tied to the subtype relation between the different 
AST node kinds/types.