Ast_mapper(3o) OCaml library 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, for-
warding of command-line flags, and storing state.
Ast_mapper.mapper enables AST rewriting using open recursion. A typi-
cal mapper would be based on Ast_mapper.default_mapper , a deep iden-
tity 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 con-
stant 42 , can be compiled using ocamlc -o ppx_test -I +compiler-libs
ocamlcommon.cma ppx_test.ml .
Warning: this module is unstable and part of Compiler_libs .
A generic Parsetree mapper
type mapper = {
attribute : mapper -> Parsetree.attribute -> Parsetree.attribute ;
attributes : mapper -> Parsetree.attribute list -> Parsetree.attribute
list ;
binding_op : mapper -> Parsetree.binding_op -> Parsetree.binding_op ;
case : mapper -> Parsetree.case -> Parsetree.case ;
cases : mapper -> Parsetree.case list -> Parsetree.case list ;
class_declaration : mapper -> Parsetree.class_declaration -> Parse-
tree.class_declaration ;
class_description : mapper -> Parsetree.class_description -> Parse-
tree.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 -> Parse-
tree.class_signature ;
class_structure : mapper -> Parsetree.class_structure -> Parse-
tree.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 -> Parse-
tree.class_type_field ;
constant : mapper -> Parsetree.constant -> Parsetree.constant ;
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 -> Parse-
tree.label_declaration ;
location : mapper -> Location.t -> Location.t ;
module_binding : mapper -> Parsetree.module_binding -> Parsetree.mod-
ule_binding ;
module_declaration : mapper -> Parsetree.module_declaration -> Parse-
tree.module_declaration ;
module_substitution : mapper -> Parsetree.module_substitution ->
Parsetree.module_substitution ;
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_declaration : mapper -> Parsetree.open_declaration -> Parse-
tree.open_declaration ;
open_description : mapper -> Parsetree.open_description -> Parse-
tree.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.sig-
nature_item ;
structure : mapper -> Parsetree.structure -> Parsetree.structure ;
structure_item : mapper -> Parsetree.structure_item -> Parse-
tree.structure_item ;
typ : mapper -> Parsetree.core_type -> Parsetree.core_type ;
type_declaration : mapper -> Parsetree.type_declaration -> Parse-
tree.type_declaration ;
type_extension : mapper -> Parsetree.type_extension -> Parse-
tree.type_extension ;
type_exception : mapper -> Parsetree.type_exception -> Parse-
tree.type_exception ;
type_kind : mapper -> Parsetree.type_kind -> Parsetree.type_kind ;
value_binding : mapper -> Parsetree.value_binding -> Parse-
tree.value_binding ;
value_description : mapper -> Parsetree.value_description -> Parse-
tree.value_description ;
with_constraint : mapper -> Parsetree.with_constraint -> Parse-
tree.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 , 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 implemen-
tation or interface.
val run_main : (string list -> mapper) -> unit
Entry point to call to implement a standalone -ppx rewriter from a map-
per, 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) ref
val register : string -> (string list -> mapper) -> unit
Apply the register_function . The default behavior is to run the map-
per immediately, taking arguments from the process command line. This
is to support a scenario where a mapper is linked as a stand-alone exe-
cutable.
It is possible to overwrite the register_function to define "-ppx driv-
ers", 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 in-
serted 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
OCamldoc 2023-02-12 Ast_mapper(3o)
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