Ppx_core is a standard library for OCaml AST transformers. It
contains:

• various auto-generated AST traversal using an open recursion scheme

• helpers for building AST fragments

• helpers for matching AST fragments

• a framework for dealing with attributes and extension points

When used in combination with
ppx_driver, it features:

• spellchecking and other hints on misspelled/misplaced attributes and
  extension points

• checks for unused attributes (they are otherwise silently dropped by
  the compiler)

Ast version

Ppx_core uses the specific version of the OCaml Abstract Syntax Tree
as defined by Ppx_ast.

Compatibility

If you want to write code that works with several versions of
Ppx_core using different AST versions, you can use the versionned
alternatives for Ast_builder and Ast_pattern. For instance:

open Ppx_core
module Ast_builder = Ast_builder_403
module Ast_pattern = Ast_pattern_403