Chapter 27  The compiler front-end

This chapter describes the OCaml front-end, which declares the abstract syntax tree used by the compiler, provides a way to parse, print and pretty-print OCaml code, and ultimately allows to write abstract syntax tree preprocessors invoked via the -ppx flag (see chapters 9 and 12) and plugins invoked via the -plugin flag (see chapter 24).

It is important to note that the exported front-end interface follows the evolution of the OCaml language and implementation, and thus does not provide any backwards compatibility guarantees.

The front-end is a part of compiler-libs library. Programs that use the compiler-libs library should be built as follows:

        ocamlfind ocamlc other options -package compiler-libs.common other files
        ocamlfind ocamlopt other options -package compiler-libs.common other files

Use of the ocamlfind utility is recommended. However, if this is not possible, an alternative method may be used:

        ocamlc other options -I +compiler-libs ocamlcommon.cma other files
        ocamlopt other options -I +compiler-libs ocamlcommon.cmxa other files

For interactive use of the compiler-libs library, start ocaml and type
#load "compiler-libs/ocamlcommon.cma";;.

• Module Ast_helper: helper functions for AST construction
• Module Ast_mapper: -ppx rewriter interface
• Module Asttypes: auxiliary types used by Parsetree
• Module Location: source code locations
• Module Longident: long identifiers
• Module Parse: OCaml syntax parsing
• Module Parsetree: OCaml syntax tree
• Module Pprintast: OCaml syntax printing

The following modules provides hooks for compiler plugins:

• Module Pparse: OCaml parser driver
• Module Typemod: OCaml module type checking
• Module Simplif: Lambda simplification
• Module Clflags: command line flags