package ppx_import

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A syntax extension for importing declarations from interface files

Install

Dune Dependency

Authors

Maintainers

Sources

v1.5.tar.gz
md5=54921e077b9de4155f7fa61db725ec6f

Description

Tags

syntax

Published: 09 Sep 2018

README

[%%import]

import is a syntax extension that allows to pull in types or signatures from other compiled interface files.

Sponsored by Evil Martians.

Installation

import can be installed via OPAM:

$ opam install ppx_import

Usage

In order to use import, require the package ppx_import.

Syntax

Single declarations

For example:

# type loc = [%import: Location.t];;
type loc = Location.t = { loc_start : Lexing.position; loc_end : Lexing.position; loc_ghost : bool; }
# module type Hashable = [%import: (module Hashtbl.HashedType)];;
module type Hashable = sig type t val equal : t -> t -> bool val hash : t -> int end

It is also possible to import items from your own .mli file.

Combining with [@@deriving]

It's possible to combine import and deriving to derive functions for types that you do not own, e.g.:

type longident = [%import: Longident.t] [@@deriving show]
let () =
  print_endline (show_longident (Longident.parse "Foo.Bar.baz"))
(* Longident.Ldot (Longident.Ldot (Longident.Lident ("Foo"), "Bar"), "baz") *)

Note that you need to require import before any deriving plugins, as otherwise deriving will not be able to observe the complete type.

[@with] replacements

It is possible to syntactically replace a type with another while importing a definition. This can be used to import only a few types from a group, or to attach attributes to selected referenced types.

For example, this snippet imports a single type from Parsetree and specifies a custom pretty-printer for deriving show.

type package_type =
[%import: Parsetree.package_type
          [@with core_type    := Parsetree.core_type [@printer Pprintast.core_type];
                 Asttypes.loc := Asttypes.loc [@polyprinter fun pp fmt x -> pp fmt x.Asttypes.txt];
                 Longident.t  := Longident.t [@printer pp_longident]]]
[@@deriving show]

For module types, the replacements are specified using the standard with construct. However, the replacement is still syntactic.

More?

If you have a use case in mind that ppx_import does not cover (in particular, object-oriented features are not implemented), please open an issue.

License

import is distributed under the terms of MIT license.

Dependencies (6)

  1. cppo_ocamlbuild build
  2. cppo build
  3. ocamlbuild build
  4. ocamlfind build
  5. ppx_tools >= "0.99.1"
  6. ocaml >= "4.02.0" & < "4.08.0"

Dev Dependencies (2)

  1. ppx_deriving with-test & >= "2.0"
  2. ounit with-test

Conflicts

None