1Ast_mapper(3) OCaml library Ast_mapper(3)
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6 Ast_mapper - The interface of a -ppx rewriter
7
9 Module Ast_mapper
10
12 Module Ast_mapper
13 : sig end
14 The interface of a -ppx rewriter
17 A -ppx rewriter is a program that accepts a serialized abstract syntax
19 tree and outputs another, possibly modified, abstract syntax tree.
20 This module encapsulates the interface between the compiler and the
21 -ppx rewriters, handling such details as the serialization format, for‐
22 warding of command-line flags, and storing state.
23 Ast_mapper.mapper enables AST rewriting using open recursion. A typi‐
26 cal mapper would be based on Ast_mapper.default_mapper , a deep iden‐
27 tity mapper, and will fall back on it for handling the syntax it does
28 not modify. For example:
29 open Asttypes
32 open Parsetree
33 open Ast_mapper
34 let test_mapper argv =
36 { default_mapper with
37 expr = fun mapper expr ->
38 match expr with
39 | { pexp_desc = Pexp_extension ({ txt = "test" }, PStr [])} ->
40 Ast_helper.Exp.constant (Const_int 42)
41 | other -> default_mapper.expr mapper other; }
42 let () =
44 register "ppx_test" test_mapper
45 This -ppx rewriter, which replaces [%test] in expressions with the con‐
47 stant 42 , can be compiled using ocamlc -o ppx_test -I +compiler-libs
48 ocamlcommon.cma ppx_test.ml .
49 Warning: this module is unstable and part of Compiler_libs .
51 A generic Parsetree mapper
59 type mapper = {
60 attribute : mapper -> Parsetree.attribute -> Parsetree.attribute ;
61 attributes : mapper -> Parsetree.attribute list -> Parsetree.attribute
62 list ;
63 binding_op : mapper -> Parsetree.binding_op -> Parsetree.binding_op ;
64 case : mapper -> Parsetree.case -> Parsetree.case ;
65 cases : mapper -> Parsetree.case list -> Parsetree.case list ;
66 class_declaration : mapper -> Parsetree.class_declaration -> Parse‐
67 tree.class_declaration ;
68 class_description : mapper -> Parsetree.class_description -> Parse‐
69 tree.class_description ;
70 class_expr : mapper -> Parsetree.class_expr -> Parsetree.class_expr ;
71 class_field : mapper -> Parsetree.class_field -> Parsetree.class_field
72 ;
73 class_signature : mapper -> Parsetree.class_signature -> Parse‐
74 tree.class_signature ;
75 class_structure : mapper -> Parsetree.class_structure -> Parse‐
76 tree.class_structure ;
77 class_type : mapper -> Parsetree.class_type -> Parsetree.class_type ;
78 class_type_declaration : mapper -> Parsetree.class_type_declaration ->
79 Parsetree.class_type_declaration ;
80 class_type_field : mapper -> Parsetree.class_type_field -> Parse‐
81 tree.class_type_field ;
82 constructor_declaration : mapper -> Parsetree.constructor_declaration
83 -> Parsetree.constructor_declaration ;
84 expr : mapper -> Parsetree.expression -> Parsetree.expression ;
85 extension : mapper -> Parsetree.extension -> Parsetree.extension ;
86 extension_constructor : mapper -> Parsetree.extension_constructor ->
87 Parsetree.extension_constructor ;
88 include_declaration : mapper -> Parsetree.include_declaration ->
89 Parsetree.include_declaration ;
90 include_description : mapper -> Parsetree.include_description ->
91 Parsetree.include_description ;
92 label_declaration : mapper -> Parsetree.label_declaration -> Parse‐
93 tree.label_declaration ;
94 location : mapper -> Location.t -> Location.t ;
95 module_binding : mapper -> Parsetree.module_binding -> Parsetree.mod‐
96 ule_binding ;
97 module_declaration : mapper -> Parsetree.module_declaration -> Parse‐
98 tree.module_declaration ;
99 module_substitution : mapper -> Parsetree.module_substitution ->
100 Parsetree.module_substitution ;
101 module_expr : mapper -> Parsetree.module_expr -> Parsetree.module_expr
102 ;
103 module_type : mapper -> Parsetree.module_type -> Parsetree.module_type
104 ;
105 module_type_declaration : mapper -> Parsetree.module_type_declaration
106 -> Parsetree.module_type_declaration ;
107 open_declaration : mapper -> Parsetree.open_declaration -> Parse‐
108 tree.open_declaration ;
109 open_description : mapper -> Parsetree.open_description -> Parse‐
110 tree.open_description ;
111 pat : mapper -> Parsetree.pattern -> Parsetree.pattern ;
112 payload : mapper -> Parsetree.payload -> Parsetree.payload ;
113 signature : mapper -> Parsetree.signature -> Parsetree.signature ;
114 signature_item : mapper -> Parsetree.signature_item -> Parsetree.sig‐
115 nature_item ;
116 structure : mapper -> Parsetree.structure -> Parsetree.structure ;
117 structure_item : mapper -> Parsetree.structure_item -> Parse‐
118 tree.structure_item ;
119 typ : mapper -> Parsetree.core_type -> Parsetree.core_type ;
120 type_declaration : mapper -> Parsetree.type_declaration -> Parse‐
121 tree.type_declaration ;
122 type_extension : mapper -> Parsetree.type_extension -> Parse‐
123 tree.type_extension ;
124 type_exception : mapper -> Parsetree.type_exception -> Parse‐
125 tree.type_exception ;
126 type_kind : mapper -> Parsetree.type_kind -> Parsetree.type_kind ;
127 value_binding : mapper -> Parsetree.value_binding -> Parse‐
128 tree.value_binding ;
129 value_description : mapper -> Parsetree.value_description -> Parse‐
130 tree.value_description ;
131 with_constraint : mapper -> Parsetree.with_constraint -> Parse‐
132 tree.with_constraint ;
133 }
134 A mapper record implements one "method" per syntactic category, using
137 an open recursion style: each method takes as its first argument the
138 mapper to be applied to children in the syntax tree.
139 val default_mapper : mapper
143 A default mapper, which implements a "deep identity" mapping.
145 Apply mappers to compilation units
150 val tool_name : unit -> string
151 Can be used within a ppx preprocessor to know which tool is calling it
153 "ocamlc" , "ocamlopt" , "ocamldoc" , "ocamldep" , "ocaml" , ... Some
154 global variables that reflect command-line options are automatically
155 synchronized between the calling tool and the ppx preprocessor:
156 Clflags.include_dirs , Load_path , Clflags.open_modules ,
157 Clflags.for_package , Clflags.debug .
158 val apply : source:string -> target:string -> mapper -> unit
162 Apply a mapper (parametrized by the unit name) to a dumped parsetree
164 found in the source file and put the result in the target file. The
165 structure or signature field of the mapper is applied to the implemen‐
166 tation or interface.
167 val run_main : (string list -> mapper) -> unit
171 Entry point to call to implement a standalone -ppx rewriter from a map‐
173 per, parametrized by the command line arguments. The current unit name
174 can be obtained from Location.input_name . This function implements
175 proper error reporting for uncaught exceptions.
176 Registration API
181 val register_function : (string -> (string list -> mapper) -> unit) ref
182 val register : string -> (string list -> mapper) -> unit
187 Apply the register_function . The default behavior is to run the map‐
189 per immediately, taking arguments from the process command line. This
190 is to support a scenario where a mapper is linked as a stand-alone exe‐
191 cutable.
192 It is possible to overwrite the register_function to define "-ppx driv‐
194 ers", which combine several mappers in a single process. Typically, a
195 driver starts by defining register_function to a custom implementation,
196 then lets ppx rewriters (linked statically or dynamically) register
197 themselves, and then run all or some of them. It is also possible to
198 have -ppx drivers apply rewriters to only specific parts of an AST.
199 The first argument to register is a symbolic name to be used by the ppx
201 driver.
202 Convenience functions to write mappers
207 val map_opt : ('a -> 'b) -> 'a option -> 'b option
208 val extension_of_error : Location.error -> Parsetree.extension
213 Encode an error into an 'ocaml.error' extension node which can be
215 inserted in a generated Parsetree. The compiler will be responsible
216 for reporting the error.
217 val attribute_of_warning : Location.t -> string -> Parsetree.attribute
221 Encode a warning message into an 'ocaml.ppwarning' attribute which can
223 be inserted in a generated Parsetree. The compiler will be responsible
224 for reporting the warning.
225 Helper functions to call external mappers
230 val add_ppx_context_str : tool_name:string -> Parsetree.structure ->
231 Parsetree.structure
232 Extract information from the current environment and encode it into an
234 attribute which is prepended to the list of structure items in order to
235 pass the information to an external processor.
236 val add_ppx_context_sig : tool_name:string -> Parsetree.signature ->
240 Parsetree.signature
241 Same as add_ppx_context_str , but for signatures.
243 val drop_ppx_context_str : restore:bool -> Parsetree.structure ->
247 Parsetree.structure
248 Drop the ocaml.ppx.context attribute from a structure. If restore is
250 true, also restore the associated data in the current process.
251 val drop_ppx_context_sig : restore:bool -> Parsetree.signature ->
255 Parsetree.signature
256 Same as drop_ppx_context_str , but for signatures.
258 Cookies
263 Cookies are used to pass information from a ppx processor to a further
264 invocation of itself, when called from the OCaml toplevel (or other
265 tools that support cookies).
266 val set_cookie : string -> Parsetree.expression -> unit
268 val get_cookie : string -> Parsetree.expression option
273OCamldoc 2020-02-27 Ast_mapper(3)