ppx_fun — shorthand syntax for anonymous functions

ppx_fun is PPX rewriter that provides simplified syntax for anonymous functions via extensions: [%f ...] and [%f_ ...].

Examples

(* anonymous placeholder: *)
List.iter lst ~f:[%f Printf.printf "element: %d" __]
(* function translated to: (fun v -> Printf.printf "element: %d" v) *)

(* positional placeholders: *)
List.map lst ~f:[%f _1 * _2]
(* translated to: (fun v1 v2 -> v1 * v2) *)

(* unused positional placeholders: *)
some_func |> [%f _1 ^ _3]
(* translated to: (fun v1 _v2 v3 -> v1 ^ v3) *)

(* 0-ary function: *)
async_func >>= [%f other_async_func var ]
(* translsated to: (fun () -> other_async_func var) *)

(* drop argument: *)
return_smth >>= [%f_ ignore_and_continue ()]
(* translated to*)

Note: function parameters are named with line info to avoid name-clashing.

Installation

ppx_fun can be installed with opam:

opam install ppx_fun

Usage

Add ppx_fun as dependency to your opam file, and this to your _tags:

<src/*.ml>: package(ppx_fun)

Differences with ppx_lambda

ppx_lambda is another ppx rewriter with aim to provide lightweight syntax for anonymous functions. With contrast to ppx_lambda, this packages is:

• Maintained %)
• Available via opam
• Uses extension syntax, so no strange conflicts/errors

Build instruction

make

to build rewriter and run tests.