package ppx_gen_rec

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A ppx rewriter that transforms a recursive module expression into a `struct`.

Install

Dune Dependency

Authors

Maintainers

Sources

ppx_gen_rec-1.0.0.tbz
sha256=477d38eb1e193611e14dc6d55af5a5dab5e6436c4a46298209d0979687e2c063
md5=e4cdce94fd2c264f7d74fdb7146dda99

README.md.html

ocaml-ppx_gen_rec

A ppx rewriter that transforms a recursive module expression into a struct.

If you write a recursive module like this:

module rec Foo : sig
  type t = string
end = Foo

The compiler treats it like you wrote:

module rec Foo : sig
  type t = string
end = struct
  type t = string
end

If you try to use ppx_deriving, you get a Undefined_recursive_module exception, because ppx_deriving generates the signature but not the implementation:

module rec Foo : sig
  type t = string [@@deriving show]
end = Foo

(* is like writing *)
module rec Foo : sig
  type t = string
  val show: t -> string
end = struct
  type t = string
  let show _ = raise Undefined_recursive_module
end

Use ppx_gen_rec before ppx_deriving to generate an explicit struct, which will cause ppx_deriving to generate an implementation:

module%gen rec Foo : sig
  type t = string [@@deriving show]
end = Foo

(* becomes... *)
module rec Foo : sig
  type t = string [@@deriving show]
end = struct
  type t = string [@@deriving show]
end

(* which becomes... *)
module rec Foo : sig
  type t = string
  val show: t -> string
end = struct
  type t = string
  let show t = (* show stuff *)
end

Usage

Just use module%gen rec instead of module rec:

module%gen rec Foo : sig
  type t = string [@@deriving show]
end = Foo

License

ocaml-ppx_gen_rec is MIT licensed, as found in the LICENSE file.

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