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doc/reason.ocaml-migrate-parsetree/Reason_omp/Ast_402/Ast_mapper/index.html
Module Ast_402.Ast_mapperSource
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.
mapper allows to implement AST rewriting using open recursion. A typical mapper would be based on 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_mapperThis -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.
Convenience functions to write mappers
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.
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.
val make_error_of_message :
loc:Location.t ->
string ->
sub:(Location.t * string) list ->
location_error