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From: Thierry Martinez <>
To: caml users <>
Subject: Re: [Caml-list] [ANN] First release of metapp
Date: Tue, 03 Mar 2020 14:20:40 +0100
Message-ID: <> (raw)
In-Reply-To: <>

I wrote :
> I am happy to announce the first release of metapp, yet another
> preprocessor for OCaml.

metapp is available on GitHub:
and via opam: opam install metapp

(metaquot is available on GitHub as well:
and via opam: opam install metaquot)

Happy hacking!

Thierry Martinez :
> Dear users of OCaml,
> I am happy to announce the first release of metapp, yet another
> preprocessor for OCaml. Similarly to ppx_optcomp, metapp is a PPX
> rewriter. But instead of introducing a specific DSL for preprocessor
> directives, metapp provides a [%meta ...] extension, where the dots
> ... are arbitrary OCaml expressions that are substituted at compile-time
> by the AST nodes they evaluate into. These expressions build AST nodes
> either by (anti-)quoting some code directly, or by using compiler-libs
> (Parsetree, Ast_helper, ...).
> In particular, this preprocessor is easy to use for conditional
> compilation, and is an alternative to cppo and ppx_optcomp.
> let option_get o =
>   [%meta if Sys.ocaml_version >= "4.08.0" then
>      [%e Option.get o]
>   else
>      [%e match o with
>      | None -> invalid_arg "option_get"
>      | Some x -> x]]
> In this example, the code between [%e ... ] is "anti-quoted": it is the
> code that is inserted (conditionally) in the rewritten module. Of
> course, the anti-quoted code can contain itself some [%meta ...]
> code. [%meta ...] can even itself contain other levels of [%meta ...]
> code for multi-stage programming.
> An example of usage of metapp is the metaquot package, which implements
> the same quoters as ppx_tools.metaquot: [%expr ...], [%type: ...],
> etc. These quoters are implemented by meta-programming: the meta-code
> introspects Parsetree.cmi from compiler-libs to generate the code
> matching the current OCaml version.
> Happy hacking,

      reply index

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-03 11:35 Thierry Martinez
2020-03-03 13:21 ` Thierry Martinez [this message]

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