An AST visitor. There is one method per AST node; override the methods for which you need to do something, and leave the others untouched.

The default operation for most node types is to pass the visit up to the node’s supertype; for example, if you override only visitIdentifier(), you will receive calls to both LIdentifier.visit() and UIdentifier.visit(), as the default operation for visitLIdentifier() and visitUIdentifier() is to delegate to visitIdentifier(). visitNode() is different: As the root of the AST class hierarchy, it has no superclass; instead, it visits all the children of the node. Thus, the default visitor will already traverse the AST fully, and if you need to perform some operation only for some node type that might appear anywhere in the AST, you can simply override that particular method and leave the rest as it is.

Note: conceptually, a Visitor is a WideningTransformer<Anything>, that is, a WideningTransformer without any result. However, for performance reasons, this notion was dropped in the 1.2.1 release, and Visitor is now an independent, unparameterized interface. See #109 for more information.