From discussion in #75, Rusthon 1.0 makes AST transformations by walking through the tree nodes one by one and dynamically generating code from to its current state and node contents.

At the same time, AST contains subtrees that are independent on parser state. Such subtrees can be described declaratively, their transformations can be separated from the walker code and maintained independently.

The role of AST matcher is to match subtrees for a given AST sequence and choose the best replacement - either choose pre-declared block or run a dynamic code on a subtree. AST matcher may also estimate necessary inputs/outputs for the transformation and request/lookup them either automatically or with human-aided supervision.