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Ast_mapper - The interface of a -ppx rewriter

Ast_mapper(3o) OCamldoc Ast_mapper(3o)

NAME

Ast_mapper - The interface of a -ppx rewriter

Module

Module Ast_mapper

Documentation

Module Ast_mapper
: sig end
 
 
The interface of a -ppx rewriter
 
A -ppx rewriter is a program that accepts a serialized abstract syntax tree and outputs another, possibly modified, abstract syntax tree. This module encapsulates the interface between the compiler and the -ppx rewriters, handling such details as the serialization format, forwarding of command-line flags, and storing state.
 
 
Ast_mapper.mapper allows to implement AST rewriting using open recursion. A typical mapper would be based on Ast_mapper.default_mapper , a deep identity mapper, and will fall back on it for handling the syntax it does not modify. For example:
 
 
open Asttypes open Parsetree open Ast_mapper let test_mapper argv = { default_mapper with expr = fun mapper expr -> match expr with | { pexp_desc = Pexp_extension ({ txt = test }, PStr [])} -> Ast_helper.Exp.constant (Const_int 42) | other -> default_mapper.expr mapper other; } let () = register ppx_test test_mapper
 
This -ppx rewriter, which replaces [%test] in expressions with the constant 42 , can be compiled using ocamlc -o ppx_test -I +compiler-libs ocamlcommon.cma ppx_test.ml .
 
 
 
 
 
 
=== A generic Parsetree mapper ===
 
type mapper = {
attribute : mapper -> Parsetree.attribute -> Parsetree.attribute ;
attributes : mapper -> Parsetree.attribute list -> Parsetree.attribute list ;
case : mapper -> Parsetree.case -> Parsetree.case ;
cases : mapper -> Parsetree.case list -> Parsetree.case list ;
class_declaration : mapper -> Parsetree.class_declaration -> Parsetree.class_declaration ;
class_description : mapper -> Parsetree.class_description -> Parsetree.class_description ;
class_expr : mapper -> Parsetree.class_expr -> Parsetree.class_expr ;
class_field : mapper -> Parsetree.class_field -> Parsetree.class_field ;
class_signature : mapper -> Parsetree.class_signature -> Parsetree.class_signature ;
class_structure : mapper -> Parsetree.class_structure -> Parsetree.class_structure ;
class_type : mapper -> Parsetree.class_type -> Parsetree.class_type ;
class_type_declaration : mapper -> Parsetree.class_type_declaration -> Parsetree.class_type_declaration ;
class_type_field : mapper -> Parsetree.class_type_field -> Parsetree.class_type_field ;
constructor_declaration : mapper -> Parsetree.constructor_declaration -> Parsetree.constructor_declaration ;
expr : mapper -> Parsetree.expression -> Parsetree.expression ;
extension : mapper -> Parsetree.extension -> Parsetree.extension ;
extension_constructor : mapper -> Parsetree.extension_constructor -> Parsetree.extension_constructor ;
include_declaration : mapper -> Parsetree.include_declaration -> Parsetree.include_declaration ;
include_description : mapper -> Parsetree.include_description -> Parsetree.include_description ;
label_declaration : mapper -> Parsetree.label_declaration -> Parsetree.label_declaration ;
location : mapper -> Location.t -> Location.t ;
module_binding : mapper -> Parsetree.module_binding -> Parsetree.module_binding ;
module_declaration : mapper -> Parsetree.module_declaration -> Parsetree.module_declaration ;
module_expr : mapper -> Parsetree.module_expr -> Parsetree.module_expr ;
module_type : mapper -> Parsetree.module_type -> Parsetree.module_type ;
module_type_declaration : mapper -> Parsetree.module_type_declaration -> Parsetree.module_type_declaration ;
open_description : mapper -> Parsetree.open_description -> Parsetree.open_description ;
pat : mapper -> Parsetree.pattern -> Parsetree.pattern ;
payload : mapper -> Parsetree.payload -> Parsetree.payload ;
signature : mapper -> Parsetree.signature -> Parsetree.signature ;
signature_item : mapper -> Parsetree.signature_item -> Parsetree.signature_item ;
structure : mapper -> Parsetree.structure -> Parsetree.structure ;
structure_item : mapper -> Parsetree.structure_item -> Parsetree.structure_item ;
typ : mapper -> Parsetree.core_type -> Parsetree.core_type ;
type_declaration : mapper -> Parsetree.type_declaration -> Parsetree.type_declaration ;
type_extension : mapper -> Parsetree.type_extension -> Parsetree.type_extension ;
type_kind : mapper -> Parsetree.type_kind -> Parsetree.type_kind ;
value_binding : mapper -> Parsetree.value_binding -> Parsetree.value_binding ;
value_description : mapper -> Parsetree.value_description -> Parsetree.value_description ;
with_constraint : mapper -> Parsetree.with_constraint -> Parsetree.with_constraint ;
}
 
 
A mapper record implements one "method" per syntactic category, using an open recursion style: each method takes as its first argument the mapper to be applied to children in the syntax tree.
 
 
 
val default_mapper : mapper
 
A default mapper, which implements a "deep identity" mapping.
 
 
 
=== Apply mappers to compilation units ===
 
val tool_name : unit -> string
 
Can be used within a ppx preprocessor to know which tool is calling it ocamlc , ocamlopt , ocamldoc , ocamldep , ocaml , ... Some global variables that reflect command-line options are automatically synchronized between the calling tool and the ppx preprocessor: Clflags.include_dirs , Config.load_path , Clflags.open_modules , Clflags.for_package , Clflags.debug .
 
 
 
val apply : source:string -> target:string -> mapper -> unit
 
Apply a mapper (parametrized by the unit name) to a dumped parsetree found in the source file and put the result in the target file. The structure or signature field of the mapper is applied to the implementation or interface.
 
 
 
val run_main : (string list -> mapper) -> unit
 
Entry point to call to implement a standalone -ppx rewriter from a mapper, parametrized by the command line arguments. The current unit name can be obtained from Location.input_name . This function implements proper error reporting for uncaught exceptions.
 
 
 
=== Registration API ===
 
val register_function : (string -> (string list -> mapper) -> unit) Pervasives.ref
 
 
 
 
val register : string -> (string list -> mapper) -> unit
 
Apply the register_function . The default behavior is to run the mapper immediately, taking arguments from the process command line. This is to support a scenario where a mapper is linked as a stand-alone executable.
 
It is possible to overwrite the register_function to define "-ppx drivers", which combine several mappers in a single process. Typically, a driver starts by defining register_function to a custom implementation, then lets ppx rewriters (linked statically or dynamically) register themselves, and then run all or some of them. It is also possible to have -ppx drivers apply rewriters to only specific parts of an AST.
 
The first argument to register is a symbolic name to be used by the ppx driver.
 
 
 
=== Convenience functions to write mappers ===
 
val map_opt : ('a -> 'b) -> 'a option -> 'b option
 
 
 
 
val extension_of_error : Location.error -> Parsetree.extension
 
Encode an error into an 'ocaml.error' extension node which can be inserted in a generated Parsetree. The compiler will be responsible for reporting the error.
 
 
 
val attribute_of_warning : Location.t -> string -> Parsetree.attribute
 
Encode a warning message into an 'ocaml.ppwarning' attribute which can be inserted in a generated Parsetree. The compiler will be responsible for reporting the warning.
 
 
 
=== Helper functions to call external mappers ===
 
val add_ppx_context_str : tool_name:string -> Parsetree.structure -> Parsetree.structure
 
Extract information from the current environment and encode it into an attribute which is prepended to the list of structure items in order to pass the information to an external processor.
 
 
 
val add_ppx_context_sig : tool_name:string -> Parsetree.signature -> Parsetree.signature
 
Same as add_ppx_context_str , but for signatures.
 
 
 
val drop_ppx_context_str : restore:bool -> Parsetree.structure -> Parsetree.structure
 
Drop the ocaml.ppx.context attribute from a structure. If restore is true, also restore the associated data in the current process.
 
 
 
val drop_ppx_context_sig : restore:bool -> Parsetree.signature -> Parsetree.signature
 
Same as drop_ppx_context_str , but for signatures.
 
 
 
=== Cookies ===
 
=== Cookies are used to pass information from a ppx processor to a further invocation of itself, when called from the OCaml toplevel (or other tools that support cookies). ===
 
val set_cookie : string -> Parsetree.expression -> unit
 
 
 
 
val get_cookie : string -> Parsetree.expression option
 
 
 
source: 2017-10-04